Boyfriend pulling on strings

I'm currently on my third IUD in two years. At first I thought my body was rejecting them, but I think my boyfriend fingering me is pulling on the strings. I actually felt him tug on the strings (accidently, obviously) this last time, and now I can feel plastic again. They're never fully pulled out, I can just feel the part of the plastic that the strings are tied to, but at that point my gynaecologist says they have to come out. Has this been a problem for anyone else? I wasn't warned this could be a possibility, I didn't think foreplay could accidently remove my birth control. I've tried different types of birth control and this is the one that's compatible with my body.