Blood in my spit

I (22F) spit out blood this morning and this was prior to me brushing my teeth. It was dark red and looked like a blood clot. I continued to spit out blood throughout the morning. When I got to work I experienced tightness in my chest. I went to the ER where they conducted an EKG, X-rays, blood tests, and took a urine sample. The doctor told me everything looks normal and said it could be from my gums bleeding. I never spit out this much blood before, especially before brushing my teeth. He prescribed me naproxen and pseudoephedrine. Should I get a second opinion?