I've never experienced metformin and carbs specifically not mixing, especially if it's happening after two years, and if you don't low carb at home, it's unlikely it's having any effect when you eat out.
Some people don't get on with metformin initially, but rarely later.
The tachycardia sounds more like a reaction, the sickness sounds like an allergy, so maybe there is a common cause, like MSG, common in chinese, but that isn't as usual on steak and chips.
Anything like pepper sauce with it?
Any other commonality?
sodium
saturated fats,
caffeine,
are other possible triggers.
Is being sick after eating out new, or have you only recently started to eat out?