Protein affect on glucose level.

[Pat91]

Or - just to suggest another spanner to throw in the works - perhaps your insulin:carb ratio needs increasing a bit for dinner? It is entirely possible to need more or less insulin to cover carbs at different times of day but because it's also more than possible that as @Pattidevans said, your basal insulin could be running out too - best to do the basal test so you can pin down as far as humanly possible, which it actually is.

Pretty certain my basal is about right because normally after my dinner I'm around the same readings as before my dinner.