Suzpots,
I recommend the following steps:
- Confession.
- Prayer to take back ground from Satan.
- Prayer to break curses.
- Hedge Prayer for Protection of Self
See the St. Pio Center for Deliverance Counseling
Help Page for more information.
As others have said here, you absolutely need to take this to Confession. What you describe may have been a mortal sin since it was a grave matter and you knew it was wrong, but did it anyway. Your consulting with the medium has opened you up to demonic harassment.
That is the bad news. The good news is that you can be restored to a state of sanctifying grace through confession, and Fr. Gabriele Amorth, exorcist of Rome explains that the confessional takes back more souls from Satan than exorcism takes back bodies.
Your biggest problem right now is not the possibility of demonic harassment. The bigger problem is that you may be separated from God due to mortal sin. It sounds like you are truly contrite; now just take it to the confessional where the sin can be dealt with.
I hope you will let us know how things are going. I will pray for you.