As a person that joined the Catholic Church in 1999 on the Easter Vigil and as a Lead Facilitator of the RCIA here is my advice.
GO TO CONFESSION!!
Scruples only get tougher to overcome without God’s Sanctifying Grace within us. Find a spiritual adviser to help after confession, for now use the Spiritual Adviser of Christ Jesus in the Mercy of His Sacrament of Confession.
All of the advice above is good stuff. Attend Mass often, go to Adoration whenever you can (even if it is before The Presence in the Tabernacle), prayer devotions are great, and Spiritual Mentors are a wonderful blessing from God.
Seek out a Priest now where ever you are, even if on the road. Let them know your situation. “I was Baptized, Confirmed, and received Holy Communion this past Easter. I have still not had my First Confession and I struggle with what is necessary for me to confess. This has become spiritually burdensome and has me struggling to decide if I am worthy to receive communion any longer. Would you please help me to say my First Confession?” I would be surprised if you found a priest that unless on the way to service someone else in desperate need would say “No.” Look up the local Catholic Church in the phone book, online, ask about the closest. Get it done make no excuses. Those excuses are the voice of Satan, the devil, the accuser and like BigRedpg51 said he is really mad about you going with Jesus to The Father’s House and giving yourself to God. He will continue to hound you until you scream “Get behind me Satan!” and enter into Confession with Jesus!
The human condition however will allow Satan to find you again after you come out of Confession which is why all the other things we recommend are necessary to keep Jesus close to protect you and keep Satan at bey. Return to Confession often, while the Church in her Precepts says once a year for Confession this is the MINIMUM standard. Those of us wishing to do things well to not just do the minimum but excel beyond that, perhaps way beyond. It is said that the Pope, the Vicar of Christ goes to Confession AT LEAST weekly. I cannot imagine a holier man and he needs Confession far more than the Minimum, in excess of 52 times more!
I do feel it necessary to correct BigRedpg51 however. There are not 3 conditions for it to be a sin. Sin is sin and always will be sin. If it is offensive to God it will always be offensive to God. The 3 conditions are what determines Mortal versus Venial. Mortal being that which separates us from God in such a way that His Sanctifying Grace (Life Giving Love) is lost from within us. This is when the only EFFECTIVE Sacrament remaining for us is Confession to renew this Sanctifying Grace. God’s other Graces can still work on us, these are which call us back to Confession, to feel the need to have Him close. The other Sacraments when “administered to us” affect us but not to give Sanctifying Grace but to provide graces drawing us back.
The 3 conditions for Mortal sin is 1) The sinner must KNOW what is being done is against God. 2) They must have truly FREE WILL to do what is being done. 3) With Free Will and Full Knowledge they must CHOOSE to do it anyway. With these conditions met it is Mortal Sin. Only Jesus can truly know our position on all three of these items, for we even lie to ourselves in our own heart. Do not presume we only lie in one direction. Some of us lie and say we do not meet all the conditions so we feel good about ourselves and do not take the steps we need to do to stay close to God, Satan wins. Some of us lie and say we do meet all the conditions so we feel terrible about ourselves and either run from God because we feel unworthy or we stay confused and take no action to return to God, Satan wins. Both of these lies know their father, Satan, and lead us to him. Better we go to Confession often, and with humble and contrite heart, place ourselves within the protective Mercy of Jesus who will take our petitions to The Father in Confession and make all things right. Confess ALL.
It is true that Mass and other liturgies have as a part of the Rite an absolution of the barrier that Venial sin brings which allows us to receive Sanctifying Grace from Sacraments, Blessings and Grace from God allowing us to be in God’s presence and to go to Heaven (likely through Purgatory) upon death. However it does not fully and properly absolve us of these sins, Confession does. If we have Venial sins since our last Confession (or Baptism in the case of First Confession) we MUST confess those as well so that they may be fully absolved. This is why I say “Go to Confession now!” You have to confess all your sins and let the priest help you sort it all out from there for your next confession.