OMG! I am so glad you posted on here!
I too have medically diagnosed IBS and am 4.5 months pregnant.
I used to take Imodium every day for peace of mind, but cut this right back due to being PG. (my GP said it would still be okay to take in small doses)
I am only taking maybe a tablet twice a week now (used to take 2 a day) and have had little to no symptoms at all!
I used to react exactly as you do after food with horrible cramps and running to the loo, but barely anything since pregnancy.
Must be the pregnancy hormone working in our favour for once!