A lot of bumps on my chest! It is super itchy when I sweat! Is it heat rash? As far as I know, I'm not allergic to anything. Help?!

Rash. A rash is best evaluated in person by a doctor for a specific diagnosis. The breast bone is a common place for rash/heat rash especially due to sweating and heat. Try a topical anti-itch cream and consider adding a non-sedating antihistamine once or twice per day until rash is gone. Keep area clean and no scrubbing.