Gaining weight too fast 😞

I'm losing my mind over here... I am 5'7" and have always been petite. I was 106 at the start of my pregnancy, I eat pretty healthy but I wasn't getting all my necessary daily calories prior to finding out (I always skipped breakfast). Once I found out I was prego, I started eating breakfast, lunch, dinner and snacks to make sure I am eating the daily calories I need to make a healthy baby... Needless to say I have gained over 20 pounds already and I'm only 17 weeks 2 days. My OB wasn't concerned about it at my last visit a couple weeks ago because I was so little prior to and I'm not living on junk but he did say to keep it to a minimum of 1 pound per week from here on out. I have gained about 8 pounds since my last appointment and that was 2.5 weeks ago! I'm doing safe exercises at home, walking about 2-3 miles a few times per week, eating as healthy as possible and I can't seem to keep it to the minimum. HELP!!! 😫