Change in cycles

So I'm normally a 31 day cycle. I ovulate on day 16 and get my period 15 days later. I can feel when I ovulate so I know my cycle very well! Well this past cycle I ovulated day 12, had a very little bit of spotting 2-4dpo and again on 11 dpo, spotted 13-14dpo and had 2 days of somewhat heavy flow and now I'm back to barely spotting.  This would have made my cycle only 27 day which is 4 days shorter than normal, but I also usually have a full blown period for 7 days. I'm not sure what to think of these sudden changes! On 14 dpo I got 2 very faint positives with blue dye tests, but when I took a pink dye it was negative. (Blue dye fails again) Any thoughts?