My son tended to only do one thing at at time, if he gained weight for a month then he didn't grow in height or vice versa. Definitely ask your ped and look at his growth curve to see if it's a consistent shape for him. My preemie son loved avocadoes and scrambled eggs around that age. I also roasted all of his veggies with olive oil and that made him excited ... still does!
I know it's so hard not to worry so express your concerns to your ped and see what he/she has to say. I've been through feeding therapy and my take away from it diet wise was to just be mindful of what my child was eating over the course of a week. As long as the foods are healthy/good calories, you know they are getting good nutrition. We started to worry when my son's caloric intake with these weekly snapshots dropped off dramatically. Even now, 4 years later, he still has days where he survives on raisins, orange juice, a banana and piece of string cheese. The next day or two he'll eat everything in site, but he's still tall and thin. I just think he'll always be that way.