What Causes Dull Pain In Chest And Breathing Difficulty When Suffering From Strep Throat?

Hello, I am a sixteen year old female. About seven months ago, I was prescribed to birth control. We decided the best option of medication was the implant, Nexplanon.. For the past four to five months, I have had mild chest pain in my sternum, this started when I developed strep throat. When I went in to have this checked on, the doctor stated it was chest wall pain, and did not do any further examination. She stated to take ibuprofen when it hurt and to try anti-acid medicines. The pain has still not stopped. About three weeks ago, I was prescribed to anxiety medication for severe anxiety, the medication being Selexa. Only a day or two into the medication I began to have dull, achy chest pain in one particular spot. Only on the left of my chest, under my collar bone, sometimes moving down into my third or fourth rib. This pain has not went away and has really been bothering me. I tried remedies such as ice packing, heating, taking ibuprofen almost daily and nothing has worked. Sometimes the heating method will work but my pain will come back right when I take the heating pad off. Just lately, my breathing has felt constricted, as if there were a bubble in my throat or something was in my airway. This has occurred for approximately two and a half days. I usually find it helpful to have a drink, most of the time water, to take this sensation out of my throat. But this sensation usually reoccurs. This chest pain is worse when I lay down or am resting. Please tell me what this could be. I am planning on going to the doctor tomorrow or Monday. But I do not know what I should do. I need advice from a profession. I need to know if this is very serious, or more on the common side. Please!