Help! My baby has hard time staying asleep!?

My baby just turned 4 months old. For the past week she has been having a hard time staying asleep. I tried swaddling her. It seemed to work for a few nights. But now she is back to just sleeping 1/2 to 1 hour at a time. I play with her during the day, I play w her till she gets tired. When I put her down for a nap, she doesn't sleep very long 1 hr the most. And at night time, ye most she can sleep is 2 hours at a time... Can someone tell me what's wrong with her?? Oh, forgot to mention she's been passing some nasty smelling gas. And when she wakes up from her naps or night time, she wakes up crying. It seem to me something is bothering her, I just can't figure out what.