First off, always REPLACE the condom after use. You ejaculate in it and then you need to change it.
It is NORMAL for you to not to be able to get erect immediately after ejaculation. It's called the "refractory period." Basically, your body needs time to recharge.
How long varies. Anxiety, probably because you thought there was a problem, can also prevent erection.
You are NORMAL. Relax.