confused

Naomi
So I've been tracking my cycles with three different apps (I was using two before discovering Glow just recently) and they are all predicting my next fertile window to be on different dates. Ovia says I'm in it now (cycle day 8 and had a negative opk today), MyCycles says starting on the 20th and Glow says on the 30th. I'm trying to catch it with an opk but am struggling with them a bit. Basically I would like to kind of know when I'm about to enter the fertile week so I could make sure we're BDing before the ovulation as well. I read about the SMEP but am worried I don't know how to follow it.. My cycles are irregular so don't think I would be able to calculate the days myself.. ugh.. 
Should we just BD every day or every other day all month long or would that not be enough?