I also had a fourth degree tear when I had my second child. My baby is now 14 months old, and I have absolutely no side effects. I don't remember how long it took for the general pain to go away (I just used ibuprofin for pain, even post-delivery), but what I did have a challenge with was scar tissue. At 6 weeks, it still hurt A LOT when anything at all directly touched down there, although I didn't have any problems sitting by that point. I think when my doctor did the 6 week exam, I almost jumped off the table. That being said, it wasn't the tear that hurt - it was the scar tissue which isn't as stretchable as regular skin. My OB said she might have to go back in and re-cut the scar to get it to relax. We never got to that point, though, because by 3 months, the scar had relaxed some. At that point, my OB gave me a surface numbing cream to help us stretch it out at home. It was uncomfortable for months, but I'm sure everything was back to normal by 8 months.
It will heal! Good luck!