I found a lump in my , what is it?

I'm seventeen and have recently found a lump in my . I can feel it at the back of my and it feels quite squishy and about the size of a g. I've been ually active for a while now and have never had any problems with anything before but this is worrying me. I'm not bleeding or anything like that and it doesn't hurt but i don't always remember it being there and i was just wondering if i should be worried about it. Any ideas?