I recently went to help a mama who was having nursing issues. The baby was several weeks old and hadn't had a difficult time nursing earlier. Her instinct was the frenulum under the baby's tongue was getting in the way of his suck, so she asked me to come take a look.
After washing my hands, I felt under the baby's tongue and easily felt the frenulum and its tightness. In fact, when he stuck out his tongue, you could see the "fork" in his tongue, typical of a too-tight frenulum.
Many midwives cut the frenulums themselves and I have been taught how to do it, but this one was pretty deep and far back, so I sent her into the doctor to have it done. She looks forward to having her nursing experience hurt much less in the near future.