Why Is My Kitten Pooping Outside The Litter Box?

I have a question about my kitten. She is 2 months old and she is constipated from time to time, but not often enough for me to worry about it. She has been going in the right direction though. I’ve been cleaning her litter box every other day or so and that seems to work just fine, but then on Sunday night, she had a bowel movement of some sort outside of the box. It was dark inside too so I can’t really see if there was any poop around her back legs anymore…but it looked pretty normal sized so far as I could tell from where we were sitting watching TV. Then Monday morning when we woke up everything came out again from the same area (the same spot). We cleaned all over again and put more litter in there and now this evening (3/24) after pooping twice like before with no problem at all – once in her box and twice outside – she has another small BBB within 5 minutes! Now this one doesn’t smell like anything unusual either; it smells kind of sour, like grass clippings sprinkled on top of cat food (which is what they ate for dinner). Is there something wrong with my girl??? Please help!! 🙁