Yes, weight can affect the dosage. So I would stick with the 2000iu the doctor prescribed and then hopefully they will retest you in two months. We usually recommend 1000iu’s for every 25lbs of body weight.
You can always come back and let me know what your level is in two months. If it is still low or not near 50ng/ml then maybe add another 1000iu for 3000iu total at that time.