I am in my late 20s, female, vegetarian. Prone to low BP/iron. Will multivitamin and mineral supplements help?

Maybe a little... Vegetarians usually have well balanced diets aside from b12 that is found in meat. Hence, a multi-vitamin would help under these circumstances or if you feel your diet could be better balanced. If you think your iron levels are low, have heavy periods perhaps and frequently feel fatigued consider getting a complete blood count and iron panel to see if you would benefit from iron supplementation.