Mark, both the spleen and gallbladder can be affected in thal minor by the high turnover of red blood cells. Next time you do see a doctor, ask for a physical examination of the spleen to see if it is palpable. Most minors will not have a palpable spleen, although the enlargement can be see by ultrasound scans. It may ease your mind to have it checked.
Being on a veg diet makes it even more important for you to take B12 daily. A sublingual B12 will help your red blood cell production, as will magnesium and natural vitamin E, and will help the RBC's live longer, which will in turn, lessen the stress on the spleen. Melon juice is also supposed to be very good for the spleen. If you like beets, they should be considered a superfood for thals.