Intermittent fasting and changing protocol

I’ve been IF-ing for 3 weeks now – 8 hour eating window with 2 meals. No sugar, no flour and I still get so light headed and irritable from 4-6pm (I eat at 12 and 8). I’m wondering if I need to either shorten my window or allow a little snack. I know in the IF video, Brooke said to give it 3 months to see progress and weight loss. Does that mean stick with the same protocol for the 3 months? She said that some clients don’t see any results for weeks. Then how would we know that we’re actually doing something that works?

So my questions are:
1- what can I do about the light headed irritability in between the two meals?
2- how long should I follow a protocol before deciding that it’s not working for me?