Welcome to e health forum.
The symptoms you have appear to be due to balanitis (inflammation of the glans penis).
Since all the tests for infections have been negative, you need not worry about them.
Avoid intercourse and masturbation for a few days. The pain and inflammation can be reduced by medications like advil or motrin. The dryness and redness can be reduced by application of K Y jelly or 1 % hydrocortisone cream.
I hope this helps.