Anxiety, overthinking and repetitive thoughts can lead to a vicious cycle in any direction they present. For example - if u have negative repetitive thought it may lead to tension and because of tension you heart may beat fast, leading to palpitations and so next you may think you have a heart problem ..... so , this is an example of a vicious cycle. Most common reason for these excess thoughts and anxiety are chemical imbalances in your brain , next it may be genetic and lastly it could be an external or internal stress. So, u can control this by using medication REGULARLY (not randomly) which are prescribed by a psychiatrist. And importantly if you also take Cognitive behavioural therapy - CBT , you will have the best results. All the very best

Symptoms suggestive of OCD. Medication must be taken regularly at prescribed dose for prescribed time period for improvement of symptoms. As you have been talking medication randomly symptoms are still there. Medication combined with psychotherapy would bring sustainable Improvement

From your brief history it seems u r suffering from OCD .Though you have taken fluoxetine 20 mg for sometime though on occasional basis. U need to take fluoxetine on daily basis and stay in touch with a psychiatrist for increasing the dose of fluoxetine .