I have the same problem, on and off. Some dives are fine. Others it feels like my head is going to explode. I usually get to descend, but it takes me FOREVER and it's irritating.
I'm going to the doctor tomorrow to get things checked out. I know that allergies are probably half of it, because my eyes have been itching for about two weeks now and I have sneezing fits, but I have no idea what I'm allergic to.
I also have some trouble equalizing my ears. Left ear is fine, but right ear sounds like a firework going off when I try to pop it. I've got some fuzziness in my right ear currently, from the last dive I took. I had ear problems when I was younger (tubes and all that stuff when I was 6).
I've been reading up on it, and it seems that some medications are okay to take (like sudafed, flonase, claritin to name a few), although most people will tell you not to. But, I want a doctors advice and the right prescription for it before I do. I also want to make sure my eustachian tubes are not all messed up. I'm thinking that a good non-drowsy decongestant may clear it up.
I'll let you know how it turns out.