Ovulation day same DAY each month but not same CD?!?!

Im now on month 11 of ttc #3....and let me tell you....im finding it extremely hard to stay positive. Ive got family members who announce there expecting and friends that have just had a baby...and every woman I see down town is either pregnant or has a new born.

So im trying my hardest to be as positive as I can and relaxed as I can be do that we dont hit the 12month mark.

Ok so my question is: Can you ovulate on the same DAY each month but it be a differnt CD?? For eg: I just went back through my log and saw that since July i ovulated on the 30th. So it looks something like this:

7/30- cd 18

8/30- cd 20

9/30- cd 17

So in theory....my ovulation day "should" fall on the 10/30?!?!

Anyone else had this happen for them?? My cycles are irregular so I find it odd that it seems to fall on the same DAY each month!

Please share you in site, it would be greatly helpful.