What Causes Severe Headaches Along With Nausea While On Vitamin D Supplements?

I recently been put on medication for vitamin d I have recently been put on medication for vitamin d defieciency and am taking 50,000 ui a week for eight weeks. Since week 2 i have been having terrible headaches along with nausea and slight dizzness. Last week i started vomiting but felt no flu like symptoms. Week 3 I immediately became naucious. Can this come from taking vitamin d? Also how quickly can you become vitamin d deficient?. I had blood work done about 6 months ago and my doctor did not say anythig about it and now when i get blood work done again im now deficient. I just do not know what to do. Ive never had health issues and its interrupts my daily activity because im either dizzy, naucious or both with a headache to follow and it does not help that my doctor (ive been to two different ones) seem so uninterested in helping me. I will also add that prior to this i was a drinker. Ive recently decided to quit and find adapt a healhtier lifestyle. Can this play a role?..any help would be greatly appreciated.