Make sure the babies diaper is changed. Sometimes they cry when they feel wet. Check your babies gums. If they are swollen it could mean he or she is teething. The main reason why babies get upset is a upset stomach you can sooth by slowly bouncing. Another reason could be the baby has gas. You can go to any store and find tiny tummies gas drops. Make sure you check with the babies doctor. The baby could also be constipated if he or she has not had a bowl movement. You can help this by giving them a little water with a teaspoon of apple juice. if you give the baby water make sure it does not come out to fast! they choke easier on water then milk.
First see if their diaper is dry and clean, they are fed, and don't have a fever. If it keeps up hold then, rock them, snuggle them. If it gets overwhelming, bundle them up like your putting them to sleep, put them in a safe place like their crib and leave the room until you calm back down. Never loose it because the baby keep crying.
well i don't have a baby but when i had to take a mechanical baby home and it was crying i really couldn't ask it what was wrong cause well it couldn't talk so i try multi stuff like giving it milk or feeding it ,singing to it,reading a book to it,watching tv with it,making silly faces,playing instrument or try giving the baby a bear or something to mess with in its hands or shake keys .