I am mentally suffering a lot due to unnecessary and negative thought are coming a lot i am thinking a lot nowadays and forgetting things i am trying to think positively but unable to control on my negative and unwanted thoughts i am literally crying?

Urge you deal with this head-on, and first find a psychiatrist. Consider starting with medication, if advised. Subsequent options might include cognitive-behavioral therapy, biofeedback training, meditation, aerobic exercise, even acupuncture.

Please see a Clinical Psychologist with expertise in multiple types of psychotherapy to help. You may need medication managed by a Psychiatrist. You may also need a physical exam to rule out any illness causing these symptoms.