I have an rx for 1.25mg of vit. d over 12 wks. i called my doctor & asked if i could instead take vit. d that was sourced more naturally from plants & not straight synthetic, which they said was fine. is vit. d3 an acceptable replacement?

You can have your doctor check the serum levels by obtaining OH-Vitamin D-3 levels (ideally would maximize about 50-70 ng/ml). Would not supplement if you are above, but most people in US are low due to sunblock. D-3 is the preferred form, D-2 is far less potent and often added to dairy products.

Unless your Vit D is very low the evidence that taking Vit D helps anything is open to question. The National recommendations are that Vit D not be measured routinely. Discuss with your D.