I have crohn's and have taken imuran (azathioprine) for a decade. i have lost 12 lbs in 2-3 months (unintentional), a weeklong headache, nausea after eating, and early fullness. should i be worried?

Sure...: But maybe a little less so if your crohn's has been in remission & has been well monitored. Nevertheless, you deserve re-evaluation of the crohn's (gut-related and extra-intestinal), your overall health, & perhaps your medication regimen at this time.

Need to see your doc: Feeling poorly for 2+ months needs to be evaluated by your doctor. This will likely require a history, examination, and lab testing at a minimum.

Maybe: Early fullness can be a sign of a small bowel stricture, especially with unintentional weight loss. You should see your doctor to be evaluated.