How do you tell if a baby is tongue tied?

My baby is 7 wks old and all along he has been swallowing so much air with his bottles to the point he has terrible gas discomfort and we have been trying to treat it with baby gas relief drops and baby bliss gripe water. He still is very fussy. It doesnt seem like he gets a good suction on his bottles or pacifier. I asked my sister in law if he could be tongue tied causing it and since she had seen a baby whose tonge was tied before she looked and thought the tie thingy under his tonge looked a little closer to the end than it should be but she wasnt sure either. Help! Thanks!