Allergies?

Hello...For the last couple of weeks I have had severe headaches around the back of my head with a lot of pressure. Also, I have been pretty nauseous and have pretty much lost my appetite. I have had these symptoms before and had my eyes rechecked and been on migraine medicine and even had a MRI of my head. Everything was normal there and my prescription for my eyes changed a little but not enough to cause headaches. The migraine medication did not to anything to help. My doctor prescribed me singulair a few weeks ago and this has not helped at all. Yesterday I got a new script for Allegra D 24 hour. Within the hour my headache went away and I was actually able to eat because my stomach settled down as well. It made my sleep difficult but I took it in the evening instead of the morning. It kind of made me feel a little loopy also. I took the meds again this morning and I don't feel as loopy but, now I still have a dull headache. Are these symptoms really from allergies? Any advice on what I should do next?
Thanks to all