Desperate!

I had a miscarriage in March and I have been ttc for 5 months! I don't understand how I could so easily get pregnant in March when I wasn't even trying, and now that I am trying, nothing! Does the miscarriage mean there is something wrong with me? I never had a D&C after the miscarriage but I did have an ultrasound and the doc said everything looked okay. I have been tracking my ovulation with a chart and been looking into herbs to boost my chances. Does anyone know which herbs are good for those of us who are ttc? Please help - I would appreciate any advice!!