DD in nighttime pain...need suggestions

I'm not sure what is going on or why, but dd (20 months) has been in pain for the past three nights (as I write this at 4:30 am!). She started Fri/Sat evening. She went to bed as usual at 8 pm and slept well until 1/1:30 am. Then she was up screaming! She was holding her bottom saying "butt hurts" and holding her legs really stiff. I though maybe she had gas and gave her mylicon. She refused to be laid down. She slept in the maya sling just fine, as long as I was walking around with her. I was able to sit in the computer chair for a little bit and nap about and hr. Then at 5:30, she wanted to go to bed and nurse! She slept until about 8, I think and was in the same pain for a little while when she woke up, but was fine throughout the whole day, including her usual 2 hr nap. Repeat same pattern last night and this night! Except tonight she's up. She is playing now just fine, but hasn't nursed since about 12:30, which is a record for her! lol I did call her ped and went in this morning. She thought it might be a strep infection on her bum and took a culture. But, I have to wait until Wednesday to be sure! I'm exhausted from no sleep or short periods of sleep sitting up with a 28 pound baby in a sling! lol, just wondering if anyone else has had this problem and what I can do to help the poor baby sleep! TIA!