Failed condom?

Maybe it’s new mommy anxiety but my husband and I have a newborn (she’s 7 weeks old today) and I just have this feeling that I’m pregnant again. We have had sex once and only once since I gave birth which was exactly a week ago and used a condom. For some reason I just felt worried afterwards but the condom seemed fine and in tact. Today I had what looked like implantation bleeding and I just “feel” pregnant. Has anyone had a condom fail and not have it break or show any signs of being defective? I know they say they are only 99% effective but... It wouldn’t be the end of the world as we want more children and want them close together but I didn’t want them this close and I don’t know if I’m ready to go through all the pregnancy stuff again! 😳 
I know you guys don’t have the answers but guess maybe I just needed to vent. 
Also, when should I test? I got a faint positive at 8dpo with my last pregnancy but I haven’t had a period since giving birth so have no idea how to track anything.