Trying to conceive after Depo shot

I was wondering how long it took for you to get pregnant after taking the Depo shot I been off it for almost 4 months right after I stopped I been getting my period every month and it lasts between 3-4 days I been taking ovulation tests but they always came back negative. Is there something else I can do like take vitamins to help my chances?? I'm getting impatient and I'm worried it's going to take forever before I can get my system back to normal