Hi Nadine,
As you've noted, your MCV and MCH both are in the range of beta thal minor. They are not close to the range for other anemias. If you carry beta minor, one of your parents is a carrier. Do you have any of the other results from your complete blood count, like Hb or hematocrit, RDW, and RBC count? Have you ever had a hemoglobin electrophoresis test done? This gives percentages of the various types of hemoglobin found and is useful in diagnosing thal minor.
Beta thalassemia is a genetic condition and in minors one of the two genes is affected. This cannot be caused by any outside force. It is only caused by a gene you got from one of your parents. This is the only way beta thal can occur. There is an alpha thalassemia that can be caused by exposure to certain chemicals, but that does not appear to have any relevance here.
Your diet is very important to your health though, when you carry thal. The better your diet, the better you will feel. Thal minor causes a need for extra nutrients like vitamin E, folic acid, B vitamins and others, so you need to make sure you get plenty of vitamins and minerals from fruits and vegetables and take supplements where necessary. Vitamin D is most important, as it affects everyone and not just thals. Unless one gets regular exposure to sunshine, vitamin D deficiency can easily occur. I suggest that anyone who is tired and fatigued have their D level checked. It needs to be at least 35.
I'm trying to answer your various questions in this one post. When you go to the mountains, the altitude causes your blood to thin and it makes it more difficult for your body to supply sufficient oxygen. After about 3 weeks at that altitude, the Hb will start to climb, but if you are there for just a short time, you will find you tire very easily.