Just using condoms as BC

Has anybody strictly used condoms as BC? I just had my second child 6 weeks ago. My two are 18 months apart. We don’t want another for at least 3 years. I had my 6 week check today and when I told her I only wanted to use condoms as Bc she kind of looked at me crazy. Then I told her that I got pregnant with my son while breast feeding and never having had a period and she called me crazy and asked again if I wanted another form of Bc. Now I’m terrified to have sex in fear of getting pregnant. Condoms are always what we’ve used now we definitely don’t want another baby for a few years.