symptoms!

Is it possible to know as soon as you've conceived? I went off BC the week before last so my hubby and I could try. My husband doesn't think it happens this fast. Buuuut. I've had acid reflux so bad the past four days yet I know it's too early to test. I spotted a tiny brown spot last week for a day but that's it.  I feel like I just *know*! I'm trying not to be overly excited...other thoughts or experiences?