Okay, you had a cold. That causes congestion. You can get water behind the eardrum when that happens. The solution is to take a decongestant. With me, when I take decongestants, it also increases my ear-wax production, clogging my ear. That also sets off a ringing in my ear. I think the first is your problem. Try the decongestant, and maybe a litte holding a hair dryer to your ear, or a couple drops of a vinegar/hydrogen peroxide mix. And seeing the doctor is always a better idea than asking people online.