Red Bump On Shaft Of Penis

I have a bump on my penis which has just come up enflamed, it looks marginly like a pimple in the way that it is red swolen 'hil' with a lighter colour middle bit. It is right at the top of the shaft where the hair stops. It isn't painfull but I know it's there and whenI touch it it is uncomfortable. I have had unprotected sex with my girlfriend but she has been checked and is clear, and she is the only person who I have had sex with before, but we havent done it unprotected in about a month and this showed up today.

PLEASE HELP ME

No GUM clinics are open near me being a sunday and what not