Ingrown pubic hair... I think its infected?

I have hair on my shaft only a 3rd the way up and couple of days ago down there started to get itchy and then yesterday I looked and I had this reddy yellow pimple looking thing on my shaft about 1cm up on the side and I think i can see a hair coming out of the head so I'm thinking this is an infected ingrown hair. It's real sore to touch. I shaved down there about 3 and half months ago that's the only time I've shaved down there. What should I do? How do I remove it if its an infected ingrown hair?