Cycle length is changing every month

Mary • 37 yrs old and just gave birth to my rainbow baby 2/22/17 after having had 6 losses and I'm expecting again on 2/9/18
I've always been on a fairly consistent 30 day cycle but the past three months or so it's changed. 27,28 and last month was a 25! Nothing drastic I agree but deff off for me and driving me crazy as I'm ttc. I'll be 36 next month and wonder if age has something to do with it? Is there anyone close to my age that has experienced this? It's kinda breaking me out a bit. My Dr said I have a good egg reserve (I'm not near menopause) so why is my body doing this?