24 male. 135lbs. most my diet is veg, bloods showed low end hemoglobin. retested few months later showed higher than usual. why is this ?

Take charge here: Please talk with your physician. If you are a vegetarian, you need to supplement. Despite all the disinformation from the "vegetarian community", it is difficult to get adequate iron, calcium, iodine, vitamin A, vitamin D, calcium, zinc, and vitamin B12. General ill-health occurs just from iron deficiency before anemia appears. Hemoglobin varies by a % or two just based on your hydration.