What do you guys think could be causing my chest pain ?

I have been experiencing chest pains that are persistent and ongoing since January so roughly four months, it first started in January when I woke up one Sunday with aching and sore chest the pain has been persistent and constant ever since. My chest also feels tight and I feel won out easy when I take my daily one hour walk, sometimes the pain gives me the sensation as though I want to cough and sometimes I do splutter, the pain is worse on the left side of the chest around the left pectoral region but spreads all across the chest, sometimes I can push around and cause pain other times I can't, sometimes deep breathing hurts other times it doesn't, there are times when it feels possibly muscular but I haven't done anything at all to injure a muscle also my chest can heavy like its congested or full of something that I've breathed in but I haven't, this feeling is worse after exercise , when I very first wake up the pain doesn't seem to be too bad but after I get out of bed it starts to creep up, I haven't found any type of patten as the pain is there constantly, the only time the pain seems to go is when I'm sleeping and when I very first wake up, I have experienced some palpations here and there such as when I turn over in bed at night or get up after sitting or laying for a while, when I get these feelings my heart increases and beats a lot harder, I have been concerned weather the issue could be heart related or not. I do not smoke and do not drink alcohol, I also only take prescribed medication, I'm 26 years old, male with no family history of heart disease, I am not overweight. Between 2014 and 2016 i had a vast amount of different heart tests and more recently about a month ago some more tests and all were normal.