Iron supplement + constipation & diarrhea at the same time help!!!

I’m 17w pregnant & just went on a slow release iron supplement last night. I’m super constipated and I have bad diarrhea at the same time!! I’ll sit on the toilet forever & only a tiny bit will come out & this goes on every 10-20 minutes! I have a two year old i can’t leave downstairs alone and my butt burns!! Help :(