Should I mention that I have a Bipolar disorder in my statement of purpose? Should I mention that I have Bipolar disorder in my statement of purpose and ask my lecturers to mention it in their letters of recommendation(I am doubtful that they will) ?

Bipolar disorder was a critical roadblock in my academic life man. When I was having maniac episode I was like "I am God, I don't need to study, I can clear this test without studying" or it just felt like I am overdosing on caffeine, I couldn't focus. When I was feeling depressed, I was just too withdrawn to study, I was almost suicidal. Either way, I was too emotional to do anything !

The aggregate GPA of my undergrad courses is 3.216 and the simple average of my last 4 semesters GPA is 3.106. It was in the last two years that I was diagnosed with bipolar disorder. I tell you its not easy managing meds and life. Most psychiatrists in India are idiots. Some of these psychiatrists even diagnosed me with adult ADD :| Its because of these drugs and incompetency of my shrinks that I feel my GPA dropped. Should I mention that too, cause in US I would even have access to better shrinks than here .. 

My GRE score is 322/340. I honestly feel I could have got a much better GPA and GRE score without this disorder man. I even got highest grades in all my practical exams too.
I would not put it in the statement of purpose as it is a forward looking document (what do you want to study, what qualifications do you have, why study at X university, etc.).

If you must include it, then the diversity statement is a good place.

That being said, I would recommend that you do not include it. You can mention that you “struggled with some health/personal issues” in college but are now prepared for university, but you do not need to give details beyond that. This is your health privacy at stake. You should talk to your letter writers to make sure they know they should  not disclose your personal history without your permission.

Once you are accepted, you can inquire about student health services and reasonable accommodation for your needs.