You need to crawl before you can walk, walk before you can run. Reality is, you need to build up to riding 125 Miles a week. Even under the best circumstances, that will be about to 2 hours a day of riding. That is a lot for a very fit person, let alone a person who has been sedentary for some time.

So give yourself a break and work up to it. Ride 1 hour a day 3 or 4 days a week for a couple of weeks. Slowly increase your time on the bike. When you can comfortably ride 2 hours without stopping, then you are probably ready to commute without being too exhausted.