confused 🤔

So I need some help ladies and it's driving me crazy, I'm pregnant with second baby and I've been breastfeeding my son since he was born. I haven't had a regular period since October of last year, so in August of this year I got my period regular flow and everything lasted 5 days, now my husband was out of town that month and didn't come until September 9 and lasted a week well in September we had intimacy and a month later which now October I found out I'm pregnant. I went to the doctor and they're telling me I'm 9 weeks due to my last period but I don't think it's true because I didn't have intimacy in August well after my period ( I swear I'm not cheating) so I just want to know has this happened to anyone? I can't figure out how far along I am due to days I had intimacy with my husband. I just know I can't be that far along. HELP!