Why Is There A Loss Of Erection When Condom Is Worn?

29, 5.7, 78 KG, MUMBAI
HI
NOW I DONT WANT CHILD SO WHILE HAVING SEX WITH MY WIFE I AM USING PROTECTION, BUT SOME TIMES I FOUND I AM HAVING GOOD ERECTION AND SAME TIME I AM TRYING TO WEAR CONDOM BUT BY THE TIME I AM TAKING FEW MIN TO WEAR CONDOM. WHEN I AM TRYING TO WEAR CONDOM I FOUND SOME WHAT I LOST ERECTION...WHEN I AM NOT WEARING CONDOM I AM NOT FACING THIS PROBLEM...ONLY I AM HAVING PROBLEM WHEN I AM USING CONDOM SO PLS HELP ME TO SORT THIS PROBLE....IS IT REALLY A PROBLEM OR SHOULD I USE SOME MEDICINE TO MAINTAIN HARDER ERECTION....AND PLEASE SUGGEST SOME WAYS TO INCREASE PENIE SIZE