Starting progress

I joined MFP a year ago or so, stuck with it for a few months, lost some weight then quit and gained about half of what I lost back. On Jan 3/13 I started again and man did I need it. With watching my calories I also started exercising. My first night I could barely do 20 minutes on the treadmill at 3 mph and a 0% incline. Tonight I did 60 minutes between 3.5 and 4 mph and 3 to 12% incline 9 ( I change it up to rest and work hard). I have also had to add more weight to my dumbells. I cant believe the differnce in under 3 weeks!