Is the condom too tight? Reason I lose erection?

SO the last time I had sex with my girlfriend I noticed that after I took off the condom there was a little red ring where the base of the condom was. I then began too put some puzzle pieces together. A lot of the time after I put on a condom I get flaccid and have to make out with my girlfriend or finger her to try and get en erection again. But sometimes it just doesn't want to get hard again. Could the reason be that the condom is cutting of circulation? I'm using standard size condoms. Trojan Intense Ribbed, Her Pleasure, Twisted Pleasure, and Fire and Ice. My penis is about 7 �" Long and a little over 5 inches in Girth. It's barely below 5�" around. Should I spend the money to try bigger sized condoms? Or is there another reason I can't stay hard?