Cycle Length Question

Al
Hi! Question for all, I have been tracking my cycles and noticing that my cycle length fluctuates. For example my last few months have been 30, 30, 26, 28 and this month I'm now at 24! I was previously counting the day I started spotting as my first day day, and have recently started counting the first day of flow, but that should only vary by a day or so. 
We have been ttc since December, just wondering if this could play a factor? Or experience the same thing or anyone else think this is normal? Any input would be so helpful! Thank you!!