Irregular cycle lengths ... Getting longer and longer?

LM :)
My cycle lenght seem to be getting longer with time, which makes it really hard for me to track O day, even with OPK
​Last 6 months:
​July: 26 days
​Aug: 25 days
​Sept: 28 days
​Oct: 27 days
​Nov: 30 days
​Dec: 34 days 
​Is this something to worry about or check out?
​We've been TTC for 8 months now.
​I've also now this month started to track BBT to try and see if this will help.
​Thanks ladies :)