So I have this red pimple on my penis but it doesn't have puss I'm 16 I only masterbate once a week now and ever since that I got the pimple I'm not a virgin I had it 6 times with both male and female and its very itchy I can't stop scratching what do I do

Plain old pimples are very common.
So are STDs.
So since you have had multiple sex partners, you need to be tested for disease.

Yes, sound like a possible STD, time to go to doctor or health department and have a check done