Not being able to come is not uncommon, at least I hope not
. I have a hard time when wearing condoms or if there is not a lot of friction. I tend to be a long laster so at times if my partner has come a few times and is at the point where the condom hurts (I have had a few partners allergic) or it is just becoming work to make me come, I will stop.
I have also had problems performing, but that was strictly performance anxiety (I was having doubts that I would be good enough to be with her, which ironically, made the performance a bad one). Once I got comfortable with the situation I was fine.
Unless it is a regular occurrence I wouldn't worry to much.