Suggest Treatment For Difficulty In Breathing

For the past few years off and on, I have a very difficult time breathing. at times its so bad I take really deep breaths and never feel like I can get enough oxygen. I also feel like I have a lot of gas in my body, but its not relieved when I belch. I also have this pinching feeling on my upper left side of my chest..closest the arm pit but in the chest. I get dizzy at times to. I have had EKG's, ultra sounds on my heart, stress tests..and there is nothing. I also can't breath laying on my back flat sometimes, and there is pressure on the back of my head. I get tension in the back of my neck and head after so long of struggling to breath. I am on day 3 now with no relief. its done this many times before and lasted days, then went away for a day or two or even weeks, then returns. I don't know what else to do? Doctors tell me I am fine, but its not normal to not be able to breath all day. There are a few times where I felt like I can breath, but it lasts minutes then its is all back. I am at a loss..and almost broke..any suggestions?