Read Nicki Doane's response:
It's always great to feel that you've found the style of yoga that most resonates with you. It sounds like you took your time and tried out a variety styles first, which I think was a great idea.
Ashtanga Yoga is certainly one of the most physically challenging and strenuous practices popular today, so I am not surprised to hear that you are feeling exhausted by it. However, I don't like to hear you say that you are "forcing" yourself to practice. That will eventually work to your detriment, and you could run the risk of resenting your practice and maybe even abandoning it.
For some reason, Ashtanga Yoga tends to attract type A personalities. I should know, since I have been practicing it for almost 20 years now! I found that after a few years of strict and rigorous practice, I too was feeling burned out. I started to mix it up and practice other things, not just my Ashtanga series. I studied Iyengar Yoga and spent more time in the poses, "researching" them, as K. Pattabhi Jois calls it. I truly do believe that doing other styles of yoga not only made my Ashtanga practice stronger and deeper, but I question whether I would have stuck with Ashtanga if that's all I ever did.
Traditionally, the practice is meant to be done six days a week, with Saturdays being the traditional day of rest. Both full- and new-moon days are rest days also. But if you ever feel like you need a day off from practice, then definitely take it! You are not a bad person if you listen to your body and your heart. Slowing down can be a really great thing. It can reinspire you in your practice and remind you why you fell in love with it in the first place.
As far as telling you what your routine yoga practice should be, I say that at the very least, do five Surya Namaskar A's and five Surya Namaskar B's, and sometimes that may be enough. If you feel like you want more, maybe do the finishing poses after that; or just the standing poses after the salutations, and then the finishing poses. Take time to explore the poses and do what feels right for you. Just make sure that you check in with yourself each day after practice and assess whether or not you feel content with what you did. I have a feeling if you listen deeply to yourself, you'll know what to do. Trust yourself!