Sex related issue. Erection. pleasehelp!

Hi, I am going through a major problem in my sex life where I am not able to do sex with my wife. The problemetic experience started last 7-8 months back. Just one fine night,when I started making love with my wife, a feeling suddenly arose in my mind that I won't be able to perform sex today and yes that's exactly happened and my erection either didn't get stronger enough or might just erection felt down. From that day onwards till date, I am not able get out of that fear that I won't be able to get erection..I also tried homeopathy medicines for erection problems. But after taking a long duration of homeopathy medicines and tjought that as I have taken medicines for these many days,so I won't get any problem. It's been a month that I stopped taking homeopathetic medicine, and the result is the same no erection and no sex since 3weeks. I also sometimes feel that I am loosing the desire to do sex because its nothing but the fear and the frustration of not getting erection.Pleasehelp