Welcome to HealingWell!
You are not alone with this IBS weight gain.... You will find at least a couple members on here can't seem to keep weight off.
BUT, because you are so young, active and healthy it makes me wonder if you have anyting else going on. Have you spoken to your family doc about
this? Have you had your hormone levels checked? Your thyroid as well?
Again, welcome to the board! Feel free to ask any questions you may have.