No period show

Hi all, ever since New Years last year I was getting my period every month since coming off the pill, my periods came this year in the months Jan, Feb, Mar, April, May, July, Sep..I’ve skipped June & Aug..my period hasn’t came so far this month & was meant to be due at the start of the month according to this app, I’ve been doing everything possible to bring on my period, but it’s still been no show..I’ve taken a few pregnancy tests & I definitely know that I’m not pregnant. Someone help with advice please. Want to get my period this month so that I can ovulate & try..