I was told breathing correctly helped so stop yawning while singing, but I don't exactly know the correct way to breath while singing so I am still yawing. So what do I do?
I have never had this issue, so first would recommend to get more sleep. Singing is a taxing event, similar to an actual run or exercise, so need to be well rested. Another thing that comes to mind is to massage the back part of the throat and gradually move the two-finger circular massaging motion forward just adjacent to the adam's apple. Supplement that with two-finger circular jaw massages right before performing.
Well it shows that you are singing in a proper way, its really normal in the beginning, just because you are lifting your soft palate, try to don't lift too much (till to get used to that position) when you are yawning you are lifting your soft palate as well and your brain gets confuse when you sing and do the same movement so try to sing as you are talking do not change your voice too much(do not try this over high notes) after this you can lift your soft palate little by little.