Babies cry for a reason
though sometimes it's nearly impossible to find out the reason. Do everything you can think of. The obvious things first like change diaper, check for injuries, feed, burp, change clothes, etc. When all else fails, the best thing to do is to hold your baby. Even if you don't know why they're crying, they still need to know that you're there. I find babywearing to be an amazing resource for this. You can have your baby close to you, and have your hands free to still go about your day. It's like a second womb for them.
They both loved going into the back bedroom in quiet and just being bounced or held. They too needed a breather.