This is probably a dermatological problem, opposed to a std related problem. You may need a physician to evaluate on exactly what could be causing this symptom. Besides, a std does not appear the next day so this is more likely something else such as what I stated in the beginning of the statement, a dermatological problem.
what kind of disease can it be? is it serious?
Hand genital contact, in your case (a handjob), is not a way for std transmission to occur. This could be something else if this was the case.
there are rashes and itches on the front of my penis‘s skin