There are several good signs here: good weight gain, passing gas, and large, loose bowel movements. It doesn’t sound like a blockage to worry about. I often see babies go through a bit of a “poop transition” around this age. They seem to go from many stools a day, to only one or less. When I see a baby like yours in my office, and my exam doesn’t reveal any worry signs, then I try the following: if formula-fed, give the baby an extra 2 ounces of water per day (just add the water to one or two of her formula bottles). If breast-fed, I make sure mom goes off any cow milk products. Usually, these make the problem go away. If not, then time to go see the doctor.