TMI-Doing the #2

Of course you have all heard warnings about constipation while pregnant. The past few times I have gone to do #2, the first second of passing it hurts, and then the rest just comes right out and is perfectly normal. The problem with the first second of passing it, well, it tears something and causes me to bleed. I am using prep H for it but it does hurt and sting. I eat high fiber foods and I take my prenatal vitamins. Why is it that the first portion is hard and painful, but the rest is softer but normal. Anyone else with this issue? Or know how I can address my embarassing and uncomfortable situation?