Sleepless Nights

I didn't take any pictures of our little muffin yesterday because I literally forgot. That's what less than 2 hours of sleep will do, I guess...

Caitlin is having a very bad streak of sleepless nights. I was reading online that other mom's are experiencing this around the 4 month mark, so I guess it's common. She goes down great, but 2 hours later, she's waking up every 30 to 40 minutes until the morning. But when she wakes up though, she's not screaming crying - it's more like a whining cry and when we go to see her, she stops and wants to either play or sleep while holding hands. We've been trying different things each night... one night I rocked her back to sleep each time she woke up. Then the next night I fed her when she woke up. I even slept with her (which actually works, but would begin another bad habit we've so far been able to avoid). Last night we let her cry to see if she would self-settle... she did for a bit, but it was a continued night of crying, falling asleep and then waking back up. What's the deal??!