Fybogel-has anyone used this??

I’m 8 weeks pregnant & severely constipated 😩 I’ve tried lots of water,walking,fruit,prunes,fibre rich foods & still nothing & I’m so uncomfortable,I feel like it’s backing up into my chest!The pharmacist said I can only take Fybogel so have had 1 sachet & hoping it will work soon.Has anyone had this & if so how long did it take to work please??Thank you