Meat and veggies aren't going to fuel you for the sorts of miles you are aiming to ride. You need complex carbs - pasta, potatoes, bread, cereal, beans, rice, etc. And a good quality energy drink may prove essential for longer rides (over 30 miles). I say "may" because everyone is different, and this is your big chance to experiment and see what works for you and what does not.

Take the next month or so and experiment with adding different foods to your diet and trying diffreent food and drink on the bike. How do you feel that day? The next day?

Sleep is critical over the long haul, so if necessary maybe experiment with an OTC aid like tylenol PM or something to ensure you get a solid night sleep every once in a while. Go to bed early and get up early. Get yourself into a schedule that will facilitate the sort of training you want to do. Staying up or out all night won't work. (I don't know if you do that but I just thought I would throw it in.)

Also, how quickly have you increased your mileage? Perhaps the tiredness is overtraining? Perhaps it is something else. Try taking a few days off and see how you feel.

Recovery is HUGE. You are not going to get better, faster, longer if you don't give yourself time to recover. Be sure to take at least 1 - 2 days a week completely off the bike. Have a day or two thrown in there where you ride at a recovery pace. You get stronger during the periods when your body is recovering.

Finally, if nothing else seems to work do check with your doctor and see if there may be some other issue such as a thyroid disorder going on.

Good luck - let us know how it goes.