What would you do?

My very happy, very smiley baby hasn't gained hardly anything in the past two weeks. His 4 month check up is in 13 days, and he weighs the same as he did when I took him in at 3 months, which I did because I was concerned about his weight gain. Hes dropped in percentiles from 70th to 22nd from birth to 3 months. The doctor said his weight gain was inconsistent but not a cause for concern. I feel like it will be at his next appt.

He eats all the time. I send him with about 20 ounces to day care from 7 am till 5, and he normally eats all of it. I asked if they thought he needed more, and they said no. He feeds from me once or twice more in the evenings, and again first thing in the morning. He sleeps most of the night, which I am grateful for, from about 9/10 till 3-5. I just don't know what to do. When I stepped on the scale with him, he was only maybe one or two ounces more than he was two weeks ago. He always seems satisfied after hes done breastfeeding. I'm so worried there is something wrong, or I'm doing something wrong.

I will say that he is teething (yes at 3 months, the doctor confirmed it) but it only seems to be making him drool more, nothing else.

Please help