Cycle Day 17 why have I not had a positive OPK yet??

Zoe

I'm on cycle day 17 and not had a positive OPK yet I do my first at around 11 which looks like it will get darker but when I do the next at around 2-3 it's lighter I test again around 6-7 and still light what is going on?? Can u have all negatives then get a positive really quickly? I've been having EWCN the last 3 days and have some left sided abdo pain and feeling bloated please someone help??