constipation and sharp bowel movements?

I'm 22 weeks pregnant and this has been happening since maybe 15 weeks, but sometimes I'll have very hard and sharp bowl movements. These poops are literally cutting my anus and I about had a heart attack this morning because I pooped and apparently got a pretty good cut! The toilet bowl had quite a bit of blood as if my period was starting but TRUST ME I made sure that not a single drop had come from my vagina! 

Does anyone have any tips to prevent these sharp bowel movements in the future??