Avoiding pregnancy - LAST CYCLE!

OK... so I'm super excited to start TTC in February. However, we have a limited number of condoms left and I just don't want to buy more once their out (I'm so sick of them, honestly). I know when my fertile window is, and I can tell when I'm clearly out, especially after reading up on it. HOWEVER, I want to be 100% confident that I can tell my husband that we are safe to go unprotected.

Has anyone conceived/know someone who conceived during the several days before their period? Based on my research, it seems it just cannot happen. I guess most people would only know the cycle in which they conceived, but I figured I'd ask anyway.