Is singulair (montelukast) only for asthma? i was prescribed it but don't think i have asthma. when i exercise i actually feel like i can breathe better.

Singulair (montelukast): is also used for a number of allergic diseases

Asthma and rhinitis: If you can breathe better during exercise, you likely have exercise-induced asthma which is helped by Singulair (montelukast). Singulair (montelukast) is also effective in reducing nasal congestion in about 50% of those treated (in my own experience) and particularly effective in controlling nasal polyps linked to aspirin sensitivity. It has been used to control chronic hives but the data is a little shaky there.