Baby Weight

My son was born at 37 weeks exactly and weighed 6 lb 6 oz. At his one month appointment he had gained 2 lbs. At his 2 month appointment he had gained 5 more! Anybody else's baby gaining that quick? He is exclusively breastfed and I know they gain weight more rapidly, but 5 lbs in one month seems to be a lot more than what's "normal". I read 1 or 2 lbs a month is expected.