Nightly crying ... me, not the babies

OK guys, I need some help here. I am a mother of one month old twins, and I think things are going well… Considering it's twins :-) for a while I was really sleep deprived and we got a night nurse so that's helping out a lot… But despite that, the past few weeks no matter how well the day has gone, I end up crying in the evening and just feeling really dark… It only lasts about an hour and I always can talk it out with my husband. So I guess what I'm wondering is from people who have experienced it… Does that sound like postpartum depression? Or is this just how everybody feels as a new mom? And also it's hard for me to leave them for any length of time with my husband because I feel such guilt, knowing twins are a lot to handle and seeing how much he already does. During the day I usually have energy and feel good and I'm able to manage the babies' needs fine.

Just FYI before everyone comments this, I am definitely planning on talking to my OB about this at my six week appointment next week. So I'm really more looking for others' experiences… Thanks in advance