[Closed] Why am I getting slower?

So this time last year, I was averaging 17-18mph for a typical 20-30 mile mid-week road ride in the Peaks. Over the summer I managed a couple in the high 18s, but then as autumn & winter came it's all gone rather downhill.

Despite riding at least once a week on road (plus a good solid Sunday MTB ride - 4-7 hours, weather dependant, some commuting stuff and some dicking around stuff), I just seem to be going backwards. I'm just back from a 35miler, which was bloody hard work (I can barely walk now) - average 16mph, and the only one that's broken 17 was a very short sprint when I absolutely nailed it start to finish and ended up in bits again. There's been a couple of rides in the 15s, and that's just downright embarassing!

So what's going on? Bike is in good nick. I'm eating well (3lb over my 10stone "racing weight", so a bit porky but not too bad), sleeping like the dead - really struggling to get up most mornings. I did have a cold 6 weeks back that took longer than normal to go, but otherwise I'm in good health. Did 3 hrs on the big bike yesterday afternoon and went bouldering in the evening, neither of which should leave my legs feeling anything like as bolloxed as they felt when I started riding this afternoon - felt more like I'd done a century.

It's really disheartening to be beating myself up like this just to end up going slower, and I really have no idea why...