Baby not gaining enough weight

Amanda
Wondering if anyone else is going through this or has any insight for me. My EBF son has continued to drop in weight percentile since his 2 month appointment from 55% to 37% at his 4 month to just 17% at his 6 month appointment yesterday. At his 4 month his doctor had me start solids once a day to give him extra calories but it must not have been enough for his percentile to keep decreasing this much. I'm now supposed to work up to giving solids 3 times a day but I just can't help but feel like I'm failing because he couldn't get everything he needed from my breastmilk. His latch is great, he eats every 2-3 hours even at night, and we have had virtually no issues this whole time I've been breastfeeding so I am beyond confused as to why he isn't gaining as much as he should. Thoughts?