I am a medical mystery

I am 17 years old and I have chronic widespread pain in my bones, joints, muscles, and skin. I have fluctuating blood oxygen (60-99) and I have shortness of breath, heart palpations, heart racing, dizziness, nausea, severe brain fog, extreme fatigue and I get pale and purple whenever it dips. It rarely stays down for more than 4 minutes at a time but it happens more often than I think it should. My primary care doc put me on beta blockers to hopefully widen my veins to help with my oxygen levels but it has yet to help at all. I check to make sure my oximeter is working correctly and that it's not just a user error. My ana test came back really high for the second year in a row. I visited a rheumatologist and they just sent me away after only doing a sed rate test. I have POTS as well but that doesn't cause low blood oxygen. If anyone can help that would be greatly appreciated because I can barely get through my day.