Feeling IUD During Sex/Fingering?

My boyfriend was fingering me last night and he told me after he felt my IUD. I got spooked thinking it slipped (again) so I was asking if he could tell if it was the strings or the IUD itself and he said he felt “the end of something.”

I’m assuming it’s just the strings, but can anyone confirm if this is normal? I’ve already had 1 IUD fail on me and if this one is too, I want to catch it ASAP

I’m also cramping today which makes me want to ask