Numbness during sex

So I’ve (F28) been having sex with my fwb (M27) for a while but it’s amazing but for some reason lately out of nowhere I feel nothing 😅 like I try to masterbate during or use a vibrator on my clit and it’s like it’s not stimulating me. This is my first fwb. So idk it’s a mind thing or what. Then when I’m in the shower immediately after I can get off on my vibrator meaning the sensation is back. 😩 the sex is so good but idk what happensssss. Maybe I’m nervous it’s been a year so idk why I’d be nervous. Idk what do yall think. I’ve never had this happen. I’ve only have 4 partners and two were ASS 🍆