I wonder if it’s heart related and not getting enough oxygen. Have you had any tests for your heart or scans. A heart blockage or irregular heart beat, and other heart issues could cause head pressure, and having trouble exercising, breathless etc. High blood pressure might also be something to consider. Do you have a heart monitor you wear on your wrist to keep track of heart beats, blood pressure, and other things. Allergies would be another consideration. I have PVC’s ( premature ventricular contractions) so had some heart tests. Dr. Said he did not see anything after a stress test. He walked out of the room and my PVCs started again. I am very sorry. Many times you have to figure it out yourself unfortunately. Keep a daily journal of times of everything you do, when and what you eat, when you exercise and symptoms you are having…everything about your day and time head pressure headaches start and when it ends. Keep the journal and maybe you can figure this out. Also record your wrist heart monitor readings several times daily especially when you are having problems.