Sudden change in periods

My cycle had been regular. Every 27 days. You know of course sometimes it'd be off to 28 days. But it was very regular.
Until 3 months ago. 
I changed nothing in my lifestyle. My weight stayed the same. I wasn't stressed. I was healthy.
Then I suddenly had a 43 day cycle... 2 weeks late. I couldn't believe it.
Well. Then the next month. I got my period on day 34 and this month was 32.
Why is this happwneing??? I mean like I've said. I have had no changes to my lifestyle and I mean even my sex life has stayed the same for the past 3 years.
& will this effect my ovulation and my chances of getting pregnant?
But most importantly: WHYYYY