Yes it could be anaemia, sleep deprivation, stress, cardio problem, respiratory tract problem etc. When it doubt it is always good to go for a simple cardiology evaluation and when you know the condition of your heart, blood flow, blood pressure, heart rate then it is easy to exert yourself. Take care!
it could be a symptom of anemia. amemia is just a iron deficiency. It makes it harder for red blood cells to carry oxygen which might be why you yawn so much, and it causes fatigue.
I've been having issues lifting too. I talked Gaspari Superpump and am not sure if this is a cause of my problem. While working out, lifting, I get short of breath or I have the urge to yawn, but cant get a good enought breath to satisfy. I started getting worried that the supplement was screwing with me but after reading about weight lifting the exertion has alot of strain on teh heart and leads to high blood pressure. Proper breathing during workouts is crucial too. I find myself holding my breath on certain sets which sends your BO through the roof. Im very athletic and do occasional cardio however when this feeling comes upon me I'm scared to overdo cardio in fear I may collapse or die from a heart attack. There are other posts on this same site that indicated shortness of breath and the urge to yawn are due to a lack of sodium in the diet, possibly stress, nueral disease etc...
Sometimes yawning can be a sign that your body needs oxygen. I don't think it's anything to worry about. The more conditioned you get it should begin to go away. Cardio may be a way to speed the progress.
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Maybe you're just not fit enough yet, and your body needs the extra oxygen yawning provides? Just an idea.