What can be the cause of middle chest pain and difficulty of breathing with upper backpain?my ecg result is normal im 25 female hav highblood pressure

Go see a doctor: It could be a lot of things either benign, or life-threatening. So you will need to get evaluated. It could for example range from anxiety attacks, to heart burn, to blood clots in the lung, to vascular problems like aneurysms of the aorta, or aortic dissection. So as you can see there are various serious issues that could cause similar symptoms even with normal ecg. Get yourself checked out.