Children and Condoms

My first experience as a teacher and a condom was when I was substituting the 2nd day of summer school at National City Middle in 2006. The kids were ridiculously behaved and one kid wanted help the whole time but I couldn't get the classroom in control to give this one child help. Finally I did and when I returned to the front of the room there was a bright red condom on the overhead projector which was turned on. I called in the VP and they couldn't figure out who it was of course. Obviously I never subbed there again.
Then in May 2008 I was teaching sex-ed to my 10th and 11th grade biology students. I had to do a condom demonstration which wasn't a problem all day until 6th period. Of course after telling all of the kids I was not distributing condoms, just demonstrating how they are used properly (on my fingers) one student asked me for one. I replied by giving him the finger. He asked for one, and I gave him one! This was followed by a parent conference where I admitted my actions and explained myself and everything was fine.
Yesterday morning upon entering my classroom I saw a bright yellow opened condom at my classroom door. Of course I left it there because I'm not going to clean it up. Later I found the wrapper in one of my classroom's sinks and threw it away. I have no idea who it was. I forgot about it until today. Towards the end of the period 1 final exam my students pointed out to me a condom unrolled with a white substance inside of it in a corner of my classroom. I have no idea who did it. I'd really like to blame all of this on the janitor who has been known to steal from about 20 classrooms on campus. But really I think it's students trying to get a reaction out of me. I really don't know what to do with this situation.
I found out two days ago that I may no longer be needed at my school and have been very upset about this. I don't want to go anywhere but here even though it is a horrible place to work there are many positives to the situation. If I am kicked out of here, I have no idea where I'm going to go and wherever it is will be further away from my baby after she's born. After these incidences I'm wondering if I really should go.