Hi there ~
I understand your concerns. I believe that you have a bruise
on the head of your penis that may be related to intercourse like you mention. Vigorous sexual activity may lead to genital bruises such as yours and the cure for the same is to wait for a week or so till the lesion heals, while keeping the area clean and dry and free from potential infections. I hope this helps. Please consult a qualified local doctor if this does not seem to be improving despite your best efforts.
Take care and have a lovely day!