I just started monitoring my blood sugar?

I've noticed every once in a while I get totally grumpy over the stupidest little thing. the last time, I had a couple double cheese burgers and I felt fine. well, I got a blood sugar monitor the other day and 15 of my readings have come out high, above 250. this morning it was 157 and now it's 545. I did just have 6 mnm cookies, that's why that last one was high, but I feel fine, and this morning I felt fine. Could someone give me a crash course on stabilizing my reading. BTW, I went on a diet as of the new year and since then, I drink 8 12 oz bottles of water during the 8 times I go to use the restroom at night.