please help!!!!

This will be long but I need help/advice. I've been To the doctor numerous times they never say anything about this until last week. For the past year my body is VERY WEAK. I have no desire to do anything sometimes I even feel like I can't think straight. Like I'm not fully there. I'm constantly tired & wanna sleep. I have a one year old daughter & I even feel like I can't be a good mom to her because I have no desire to do ANYTHING. It's gotten to the point where I'm depressed about it. I stand up & I get really dizzy. I black out for like 10 seconds. My doctor told me I have vitamin d deficieny. & too much potassium. He just told me to take vitamin pills. Has anybody ever had this too? What can I do to help my body recuperate faster? I literally live off of energy drinks because I have ZERO energy to do anything. (Which they don't help. I'm tipically a very energetic person)