Breastfeeding weight gain?

Hey mommas! Question here! My daughter is 13lbs at 5.5 months old. Her birth weight was 7.1lbs and when we left the hospital her weight was 6lbs 13oz. We exceeded her birth weight within the recommended 2 weeks. since then she has always slowly gained weight. I am a first time mom and I'm just wondering if all breast feed babies gain slowly or on average? I'm a very small gal and her dad is a medium built guy. I'm 5'1 and 135lbs. My daughter is 75% for height, 11% for head circumference and was 3% for weight at the 4 month check up. She is getting taller, meeting her milestones, plenty of diapers and in 6-9 month clothing. I guess my question is, does she weight enough? I didn't see my daughter's original doctor at the 4 month and that doctor told me to start supplementing with formula. I feel my daughter is very happy and healthy. She started solids at 5 months and just recently she hasn't gained any weight like the passed week. Normal? sorry it's all over the place. just a lot of questions!