ttc is a struggle😓

ok so having a hard time understanding when my fertile days will be. my last period was.july 10th.and lasted 5 days like usual this app it shows in green which I think is my ovulation days to be from the 20th-26th, but I keep being told it would be 28th,29th,30.. I have no idea how to track this stuff and do all that counting its soooo confusing!! I have 2 other kids got luckywith them cus I never even tried to get pregnant so I didn't have to go through all this, they was just my blessings from above😇😍