I'm 15 and I have a reddish and looks kind of like a pimple on the side of my penis but its sort of big like 1cm all around I have had sex once unprotected the other times I used a condom I'm worried its like cancer or something like that and don't want to tell my mum or go to the doctor unless a girl doctor checks it out witch is unlikely give me an answer

Sounds like you could have genital herpes. Look up genital herpes photos online and compare your lump with the photos. If it looks the same, then you more than likely have genital herpes. The one time you had sex without a condom was all it took to get this. In the future always use a condom. And herpes is not curable - it can only be controlled and tends to reoccur and you can spread it to females quite easily when you are in an infection stage of the sores.