Feeling so defeated....

So my husband and i have been ttc since june, i really need someones opinion bc im tired of calling my doctors office every month asking questions! Last month i was a week late, AF came for a day... went to the doctors and they said negative on the pee and i declined the blood bc i felt defeated... so we talked about when is the best days to BD during my cycle day 9 to 21 every other day is what he told me... so we did! I started to spot very VERY lightly 11/24 a little more on 11/25 we got excited bc that was 12 DAO so we thought is was implantation bleeding... then AF showed up 3 days early for 2 days... so why is my cycle changing month to month!!!!!!!