Firstly with blood glucose readings that fluctuate like that, you need to be in more control, the principle way of gaining control is by finding out how what you eat affects your BG, the only way you're going to do that is by...testing.
Speak with your GP, ask them to prescribe more test strips in order to find out what's going with your BG. If they refuse refer them to NICE guidelines (summarised here) and also this. If they still refuse, ask your pharmacist if they know of a GP who is prescribing test strips and transfer to that practice.
Ask to be referred to a dietitian as well.