It makes sense as solids (especially introductory solids) do not have as much calories as bm. When you say he's starving and feeding from both sides is this during the 7pm feed? If so, there's nothing wrong with him feeding extra during the one feed, he is getting bigger so it makes sense that he needs more. I would be more concerned if he started waking for extra feeds or wanting additional feeds in the day but not concerned with him wanting more during one feed. My dd always fed from both sides and (I hate to tell you this) we were never able to drop the 5pm bf, we kept it for ages! We dropped the 3pm feed first (when she was much older, well established on solids, and dropping bfs), we replaced it with a solids snack, then we dropped the df, then the 7pm feed.