If you suspect that your baby is tongue-tied (has a tight frenulum, or attachment, under their tongue), it is best to have them evaluated as soon as possible by someone familiar with various types of tongue-tie and how it affects feeding efficiency for baby and comfort for mother. Many babies can breastfeed even while tongue-tied, but it may take them much longer, and they may have difficulty getting the milk they need to grow well. They may also cause a great deal of pain and possible nipple damage for mom since they are unable to move their tongue properly during feeding. An experienced IBCLC (certified lactation consultant) can evaluate your baby's ability to transfer good quantities of milk and make sure that your milk supply is protected during this process.
You may want to see your baby's pediatrician. Most tongue-ties are very easily released by a simple in-office procedure, after which your baby can immediately go to the breast.