Drowning. I am all alone.

I have a 17mo old and a 4mo old. My husband travels at least half of the month for work. I'm having a really hard time handling the two kids, especially from about 5pm on. Someone is always crying. It's hard to soothe the toddler to sleep in his crib, especially when I have an infant cluster feeding, for example. Someone always needs me and I'm out numbered. I literally can't keep everyone happy. What do I do?