Help me!😭

Ok so I noticed this lump under my skin about the size of a pea in my groin area. It's really scaring me because I have been sexually active in the past only with one guy and that was my ex. He said he was tested multiple times and they all came back negative and he didn't have anything. However it's still really scaring me and I tried telling my mom about it and she has just kind of been brushing it off and it has really hurt my feelings. Can someone please help? I'm 17...