During pregnancy, your body release progesterone that helps to relax your body's smooth tissue. This helps maintain a healthy pregnancy but can also increase gas -- burping is just part of it if you get my drift! :)
If you notice certain triggers for extra burps -- for instance, carbonated beverages or spicy food -- try eliminating those from your diet to see if it helps.
If burping is causing pain, or if you have any other concerns, talk to your OB or Midwife.