Large bump on testicle, what to do?

I have had a bump in the same spot on my testicle for almost 2 year now. It often changes in size, sometimes seemingly completely dissapearing and other times getting almost as large as a dime. Yellowish pus usually comes out of it if i squeeze it but none will come out right now. What should i do and how concerned should i be. The picture attached is how it currently looks. Ps I am 18 so the bump first appeared when I was 16.

it’s a cyst. theres probably a hair trapped in it. it’s not an std or anything. talk to a dermatologist