Do Universities go through old assignmnets to check for plagiarism? I am new University student, in software engineering program.
I was FALSLY accused in plagiarism in my second semester and it resulted in a 0 on the assignment of course. I believe a student copied my code while on an online study group I initiated, but because I was pregnant and gave birth a couple of days after the accusation, I didn't have it in me to fight it, as I needed to appeal and the whole process would have taken probably a couple of months and I couldn't take the stress. 

So I just took the punishment and "admitted" I plagiarized. Needless to say, it was the most stressful, terrifying time in my life, I thought my academic career is over for good. Of course, I learned from my mistake and  I stopped helping people through study sessions all togather as I have my family I need to think about, and as I have two babies and I am exhausted all the time it is very easy for me to not pay attention to things. But since then, I am absolutely traumatized and can't stop trying to think whether or not this might have happened to me before and I just happned to not get caught and the thought about this possibility is absolutly killing me and I find my self up at night thinking about it and it is really starting to destroy my life. 

My question is, and it's only an hypothetical question as I only started with the study sessions that semster and stopped immediatly after being accused, what happens if god forbid someone coppied my code in a different course before and we just were not caught for some reason? do universities usually go back to check old submittions for plagiarism? 

I am absolutly terrified, so much so that I am considering dropping out. 
I know my fear is not rational but I can't control my thoughts and it's driving me crazy, I need some reasurance. I am terrified to work so hard for my degree, just to have it revoked by the university at a later point.

By the way, I take full responsiblity for my mistake, I realize that I should have never put myself in a position where I was at risk to accidently share my code with another student.
Don’t worry,

Just don’t do it or anything like it again.

You were punished for that infraction and they expect better of you now. As a lecturer I don’t go back through all old submissions as I don’t have time..

Just do your best from now on and don’t give up.

Best wishes.