Hello, I'd like to help you with your question.
From the symptoms you describe, it sounds like you might have Bipolar
disorder, possibly Type II. That is because you are having periods of extreme highs and periods of extreme lows. It could be aggravated by other disorders such as Autism, but extreme highs (feeling good, on top of the world) and extreme lows (no motivation, depression) are signs of Bipolar disorder.
You are getting too many conflicting reports from doctors about what you might have and that does not help you seek the right treatment. It's like going to the doctor with a pain in your side. It could be a pulled muscle or appendicitis, but until you know for sure, you don't know how to treat it.
Your first step should be to find a professional who can provide an accurate diagnosis. To find a good therapist, talk with your regular doctor. Or use this resource to help you:http://psychcentral.com/blog/archives/2010/01/26/10-ways-to-find-a-good-therapist/
Also, talk with anyone you know who has had treatment about their experiences. If you don't know anyone, you can contact your local university and hospital for recommendations. Usually, nurses can help as well since they work with many doctors and know who is the most qualified.
Consider researching Bipolar yourself as well to see if you fit the symptoms. You know best what you experience so you can often find out yourself what you might have then have a professional confirm it for you. Here are some resources to help:http://www.helpguide.org/mental/bipolar_disorder_medications.htmhttp://www.helpguide.org/mental/bipolar_disorder_diagnosis_treatment.htmhttp://www.helpguide.org/mental/bipolar_disorder_self_help.htm
I hope this has helped you,