My son's Ritalin

My is 15 and currently on Ritalin for his ADHD (Do not start with me. This has helped him the best and he's on low dose so keep anything about that to yourself. IDC). He came up to me and said he's almost out which doesn't make sense because he got his new prescription two weeks ago and he had a months worth. He has like 4 left.

I really don't want to accuse my mom. She was over here. She is a drug addict although claims she's sober now. I was never raised by her because I was taken away at first because she went to jail for abusing my brother. She stole from me in the past. Lied about a pregnancy saying an 18 year old raped her and got her pregnant. That was all a lie. She told me she's sober now and she wants to be better and be back in our lives and our kids lives. She was over here on and off the last few weeks and my son's medication isn't locked away. It's in our medicine cabinet in the bathroom. I don't want to accuse her when she's claiming she's trying to be better. But it's suspicious.

Edit: My sons pills go in a weekly pill counter and he puts more in every Friday. He went to open his bottle this morning and noticed there were only 4 left and that's when he told me he was almost out. He doesn't know what happened to the rest. Which I do believe him when he says that