How do I regain my sense of smell?

This is a very unfortunate thing to have had happen, as the sense of smell adds much to life. There are several things that can cause a loss in the sense of smell (anosmia, as it is known to doctors), but it would be unusual for there to be a surgical correction (with the exception of any disease that might have been caused by your long history of allergies). The general advice is to continue with exactly the same medication protocol that you are currently using, i.e., a nasal steroid, antihistamine, or whatever works to clear your nasal passages of the normal allergic symptoms that afflict you. Once this has been completed, and after the passage of time, there is often significant improvement. If some time has passed and your nasal passages have been clear, or if you have abruptly noted a change in your sense of smell, then you should visit an otolaryngologist (ear-nose-and throat surgeon). They will likely perform a test to determine how well you are able to smell, if at all, and then recommend further testing. They will also examine you to see if you have any nasal polyps or other abnormalities that often result from the inflammation that occurs with allergic rhinitis. If you do have nasal polyps, many people do have improvement in their smell with surgical correction.