TTC and periods getting later when normally clockwork

I am getting more frustrated as the months pass and I am really trying not to!! Me and my husband have been TTC since September 2009, so I know in the grand scheme of things not as long as some people. I havent been on birth control so don't have that to hold me up & my periods are (were) as regular as clockwork! That is until the last 3 months where I have been late, last month being the worst as I was a week late to the day!! My friend even talked me into doing a pregnancy test, which I had decided I was never going to do until I was a week late, negative obviously & came on next day!
The main thing that is frustrating me is my periods, I keep telling myself its a good sign & must be my body adjusting, hopefully.
We are trying about 3 times a week, trying to work on the every other day basis! My best friend has PCOS, and after over 2yrs of TTC found out she was pregnant in Nov, so I know all the advice the docs told her while TTC.
Any way keeping fingers crossed maybe this month, 1 day late (!), but obviously not getting hopes up to much!