Really constipated, what could be wrong? (very discriptive)?

For the past week i have had constipation, whenever needing to go to the toilet, only gas comes out. I have been really straining, i know that is bad. For 2 days now, i hav been able to go i little, but the part around my anus is really hurting, like a stabbing pain, whenever anything comes out. Plus all around my bum, the cheeks and my vaginal opening is really aching. example like ive been tearing myself in two. What could it be? Just really bad constipation?