Hello Doctor, I Am Aged About 45years. I Got Married

Hello Doctor, I am aged about 45years. I got married in 1997. Blessed with 2 kids, one is 16 and other is 14 years. I have sound health, weight -ft 5'.11" inches and weight - 77kgs, No BP & diabetes, I do exercise, exercise is my hubby. I am fond of sex. Since after my marriage there was no problem in sex and I could do sex 3/4-times daily till march-2014. Whenever I touched/caught/approached my wife/partner surprisingly my penis found strong and hard erections even after the ejaculation it was remained strong for half or one minute which was more pleasure to both. I used to smoke cigarette for last more than 20-years, which I have already given up from October-2014. In the month of March - 2014 I felt sprain on waist for which I took two tablets from a druggist without prescription of Doctor, as a result since that day I lost my erections power. During sex penis erection is very slow and loose. Due to looseness sex is not possible. Some times during sex it became lose. Second intercourse in a night became curio. Please advise, how can I regain my past sexualpower and perform like teenagers. I need hard strong and long lasting erections.