AA weird feeling down there

Hey guys, i want to ask a question about something. I get this weird feeling in my uterus when i poo. It feels like a ball but it gives me a tingly funny feeling. I am sexually active but we use only condoms. My period starts on the 20th/21st. Any ideas on what it might be? Thanks.

Update: I don't know if this app has age restrictions but i am 19 if that makes any difference.