My legs are fatiguing abnormally fast at the moment, like within a mile they become much slower and heavier. I did a half marathon yesterday and it was the hardest run I have ever done. Got just under 2 hours, but in the last few years I could do this between 1.25 and 1.35 depending on training and course.

Some history:
I did a 50k in december last year, after that I got pretty sick for a week. Then for 6 months I didn't really run too much. Once a week, never felt good but I thought it'd just be because I was running once a week. Then four months ago I slowly started to ramp it up more. Didn't feel good but I just thought be patient. Have been running 4-5 times a week. BUT I never improved, my legs always felt very heavy and fatigued. Didn't experience any improvement in fitness, or in comfort when doing just a simple short easy jog.

Last week I got nervous about the half marathon and got a massage in a desperate attempt to get some power back in my legs. Apparently my hips were very tight, but then that didn't seem to help much on sunday...

Has anyone else experienced this sort of thing? Any particular issues?