Dealing with constant spit ups can be annoying, but if baby is gaining weight well and doesn't seem to be bothered, you might not need to do anything (besides a lot of laundry).
Here are a few factors that can lead to frequent spit ups:
•Sensitivity to something in your diet (cow's milk is the most common culprit)
•Sensitivity to something in baby's diet: Have you fed baby anything other than your milk?
•Swallowed air: Fussing and crying can cause baby to swallow more air, which can in turn cause spitting up.
•Teething: Teething babies drool more. Swallowing this extra saliva can cause spit ups.
•A cold or allergies: These can cause baby to swallow mucus, which can lead to spit ups.
•A growth spurt: Sometimes babies swallow more air during feedings during a growth spurt.
•An oversupply of breast milk or fast let-down: Sometimes baby takes in more milk than she can handle — and the extra comes back up. If this is the case, you can help by working to lower your milk supply a bit.
•GERD (Gastroesophageal Reflux Disease): Some babies have trouble with stomach acids coming back up through their esophagus. A doctor can perform certain tests to diagnose the disease.
If baby isn't growing well or seems sick or uncomfortable, talk to your doctor — she should be able to help diagnose the problem. And if she's happy and fine? You can experiment with a few tricks, like feeding baby more frequently (for smaller, easier-to-digest meals), allowing baby to completely finish one breast before switching to the other (which puts more fat and less lactose in baby's gut), and eliminating certain foods (like dairy) from your diet. You can also have a lactation consultant (IBCLC) check out baby's latch — a good, deep latch minimizes air swallowing and can lead to less spit ups.