You need to understand that confessors typically hear the same sins from the same penitents over and over. Once we have formed an attraction to a particular sin, it can become like a trick knee: that is, something we have to learn to take care of in order to avoid re-injury.
If you had a physical health issue that you continually exacerbated through your own fault, do you think you would heal faster if you bounced from doctor to doctor, pretending to each one that you were experiencing this injury for the first time? If you were to do that, your desire to avoid a sense of shame would make it less likely, not more, that you would learn how to avoid re-injury in the future.
You do not have to return to the priest who first heard your confession. The main thing is that you actually do go to confession. Having said that, it is probably better for your spiritual advancement if you form an ongoing relationship with the same confessor, just as we prefer to do with doctors of the body, and for the same reasons.
As for altar serving, you also have the option of serving at the altar but not receiving Holy Communion when you are aware that you are not in a state of grace. It is OK to assist the priest and touch the sacred vessels, because you are fulfilling an obligation and your help is needed. If the priest can only hear your confession after Mass and not before, that is an option to consider. Get to Mass as soon as you can, catch him and say bluntly, “Father, I have something urgent and private to ask you. Could we talk now?” Be very direct, but then once you’ve made yourself clear obediently do as he says.
Yes, it is, sad but true. I think I’ll ask the priest to pull me out for 2 min for confession.
The same thing happened a week ago, will he think badly of me after?
A physician treats a recurring problem differently than a one-time issue, but he typically does not “think badly” of the patient whose problem is recurring and frankly, it is irrelevant if he does. What is important is your return to grace and your chances of staying in that state once you get there. Give your physician all the facts, so he can give you the most appropriate course of treatment and therapeutic advice.