Sometimes when they are teething they aren't as interested, same with ear infections (although sometimes they want to more for comfort when they're teething so I guess it depends on the dc).
DD did the same thing when we started solids and recently my milk supply is so low (can no longer pump extra and dd's not having many wet diapers) that I cut a little bit of solids out so she'll nurse more. She was nursing 5x/day and doing great the first 5.5 months of her life. Recently she's only wanted 4 with solids, which would be fine by me if she was wetting and didn't seem constipated. I talked to one of the nurses at her pedi's and I'm now nursing as much as she'll take it and cut out her daily snack and practice water in her sippy.
ETA-sorry for the long answer and I hopefully your DC and milk supply will be fine. DD also became a more efficient eater and was able to go 3.5 hours instead of 3 at that age.
It could be the solids. Are you nursing before or after you give him solids? Is he teething?