All of a sudden my right arm started feel heavy and weak and a pain was in the right side below collar bone the chest pain is gone. pregnant also?

Are you pregnant?: It is not clear if you are saying you are pregnant or wondering if you might be. If you think you might be pregnant check then check a home pregnancy test. They are cheap, reliable and available at any pharmacy. The pain you describe is odd for a 26 year old. Monitor to see if it return or if other odd neurological symptoms appear. If so report it to your doctor for testing

Arm weakness: While serious conditions like stroke and heart attack are not common among young people, they can occur. Chest pain needs to be taken seriously and evaluated by a doctor if it is concerning to you. Similarly, sudden weakness on one side could indicate a stroke or other vascular problem. Get checked out immediately.