same thing happened to me last year. i was averaging over 100 miles per week, then had a bad chest infection, which then turned into blood clots on both lungs and left leg, i struggle to do more than 15 miles these days, and now im back on antibiotics for another chest infection, i wont let it stop me going out on the bike though, it just means more coffee and pub stops, and on a bad day strongbow n painkillers lol, seems to get worse with the cold weather, so probaly gone get a scarf to put over my mouth when riding, so the cold air doesnt go straight onto my lungs, hope this helps.