Why might a 10th grader be absent from school for 3 months?

I've been in a day treatment program for the past 3 months and am going back to school next week. In my program, people have discussed things they could tell their classmates once they returned to school, but they were all absent for like 1 month at the most. I've been absent for 3 because my bipolar disorder had me all over the place until I was eventually stabilized on medication.
I was wondering if there were any other logical possible explanations. I don't plan on making up a lie and spreading it; if people ask me, I plan to just tell them that I was absent for personal reasons or "It's not important."
I doubt that my classmates will guess exactly where I've been, but I was wondering if they could have any other ideas in mind as to where I've been.

Might they think you were pregnant? Three months would be about the right time to be out. I'd say I was helping care for an ailing grandmother, aunt ... whoever fits. Then say it's upsetting to talk about. But kids are mean--if you don't tell them, they will make something up.

My opinion. Im bipolar II--if i can do anything to help, let me know. Take great good care of yourself.

roadie

Ahhhh, I didn't even think about that. Someone started a rumor that one of the girls in my program was pregnant because of her 1 month long absence. According to my friend, right now the people at school think I transferred schools. But that theory will get disproven obviously once I come back next week.
Thanks so much for the suggestions and everything!

I would just say you transferred schools didn't like it and came back. That could work. It makes the rumor fit so it's more believable.

I'd go with that. Say you transferred and didn't like the other school so you came back. Good luck!

Yeah, the transfered school is a good one. Since you were in a day treatment with other teens, it was technically true. Just say it was a "private school" if anyone asks.

The transfer is a good one. and you wouldnt really be lying.

the "school" you went to for those 3 months just had a different curriculum, mainly psychology and behavioral studies.

Best wishes and good luck

Thank you guys so much for your suggestions! They really meant a lot to me! I just thought I'd update since I went back to school on Thursday. My teachers made it kind of obvious that I didn't switch schools and that I was on some sort of home instruction; one of them talked to me across the room about the stuff he "sent me" (sent the program) and another apparently said something a couple weeks ago about how I was coming back soon. One of my teachers even curiously asked me who my home instruction tutor was (he thought I was in normal home instruction, like someone came to my house) & if it was someone from my school & if I liked them, and I awkwardly said that I was in a program and there were a bunch of different teachers for different subjects so I just did my work and asked the teachers if I had questions.
My first day back was great really, I received a lot of personal recognition for coming back. My first period class clapped for me when I came in and someone in my Spanish class drew a "Welcome Back" crown for me on the board (they usually draw "Happy Birthday" crowns for people on their birthday). And in most of my other classes the teacher and kids acknowledged my return and welcomed me back.
Actually, nobody asked me where I was on my first day back. They just welcomed me back. The only person that asked me where I had gone asked me yesterday, on my second day. I was standing outside waiting to go into my English class and my friend (that knew what was going on with me) asked me if I got to sleep in a lot while I was in the program, and I told her about how I got to sleep in until like 10 everyday & then another (nice) girl looked at me and was like "Oh yeah, where were you all that time, if you don't mind me asking?" and we were right about to go in so I just said "Oh...uh it's complex" since it'd be obnoxious if I said that I transferred but at the same time I got to sleep in until 10 everyday.
But overall I think everyone pretty much knows that I was on home instruction, but not the actual reason, and it seems they don't want to seem nosey and ask. I asked my friend if there were any rumors about where I'd been, and she said no but everyone was curious. But it seems no one wants to ask me to my face, so I guess I don't have to worry about making up excuses or anything.
Thank you guys so much for your wonderful advice, and for being supportive! You're all awesome!

I think it went very well. It must have felt nice to be welcomed back this way!