We aren't doctors. If you can't afford one, find a clinic that will help you. Asking about medical symptoms on social media could get you "advice" that could do you more harm than good. Get help!
Do I have a problem? I can very easily mess up my breathing pattern by simply thinking about it. Then, afterwards, instead of my brain breathing FOR me, have to do it myself, and it tires my lungs easily and I feel like I'm not getting enough oxygen even though I was just fine 5 minutes ago. Am I okay???
I don't know if you're okay, but you should really go see a doctor. It could be something serious, or nothing to worry about, but I wouldn't want to take any chances.
There is the saying "If you can't breath, nothing else matters."
Conscious concentration on what is an automatic action of our body can interfere with that automatic operation---and that can have either a positive or negative physical effect on us---especially in the short term.
And especially if you for whatever reason are thinking you are NOT getting enough air.
If you can't get to the doctor, a pulse oximeter is a medical device that indirectly monitors the oxygen saturation of a patient's blood (as opposed to measuring oxygen saturation directly through a blood sample).