Need advice on iron deficiency and feeling exhausted

Hello I just previously had lab work about 3 weeks ago and it took my Doctor awhile to give me a call and let me know the results. The results showed that I basically had no iron in my system it was almost non-existent. So I waited for the iron pills to be sent to the pharmacy for almost two weeks and my husband called the Doctor and the Pharmacy several times and nothing had been done. So I had my husband call the nurse and ask if I could just get something over the counter and she said that was fine. So he got me the 325 mg tablets So my question is how many pills should I take and how long will it take to feel better. Because for almost 3 weeks I did is sleep and it's continuing like that. I get exhausted just taking a shower. I am not usually like that so after a couple of months I finally said something to my Doctor and that is when she sent me to get the labs done. So at the risk of repeating myself I just wanted to know how long until I feel results I have been taking the supplement for a week now. T.I.A for any information you can give to me.