Hello,my Problem I Am Not Getting Erection When With Wife

Hello,my problem I am not getting erection when with wife for sex, though tried to work with hand,it gets erected and becomes normal before I insert in her vagina.due to this she is upset, and saying ur not having stamina.Due to this I have checked semen analysis test done and it is OK,I have 70million sperm.There is no problem of infertility. What are other test to be done or to use ayurvedic medicines like vita-ex gold plus.or natural things to improve.Pls help me what to do now
I'm 32 yrs,she is 20