I had canker sores for years and years when I was younger (started in my teens). Hormonal shifts can also trigger them. I did not show signs of Crohn's until I was 34 years old! So, don't worry too much. Lots of people have canker sores who never get IBD.
--40 year old female, dx as UC in '04 (1st symptoms in '03), switched to Crohn's in '05, 1 fistula, crohn's colitis, limited to large intestine
--rejected (reaction/didn't work): Asacol, AZA, 6-MP, MTX, Remicade, Humira, prednisone
--methylpred - finally off 6/15/08, tried Prochymal in Phase III study (can't wait til it's approved!)
--started Tysabri 3/21/08
--single mom to 10-yr-old girl