It is impossible for you to have conceived in September - 4 months ago - and have had a period in November, and be 3 weeks pregnant. Here is a good guide to get you started on figuring out when you might have conceived: https://www.medhelp.org/posts/DNA---Paternity/FAQs----Who-is-my-babys-father/show/3035989
I'll let others answer about acid reflux - it has been many years since I've been pregnant!
Jan, if you have clockwork 28 day cycles you most likely got pregnant the week ending Nov 17th. A first trimester ultrasound will give you an even better handle on that, but remember that "weeks of pregnancy" dates from your last period and not from the ovulation in question, which is 14 days later.
I believe that test only indicates as far along as 3+ weeks so even if you are 8 weeks, you would see 3+ on that test.
The first day of your last period would be considered to be your first day of pregnancy (you only conceived about 2 weeks later but # of week pregnant starts from the first day of your last period). Depending on your cycle that can change dramatically if you have an irregular cycle but you will find that out during an ultrasound. As for the acid reflux, I was told to take tums. It may be worth verifying that with you doctor though as there are so many different kinds of tums, I would want to double check that they are all safe before taking them.
Because I tend to avoid any medication, I had warm water and milk mixed together for my acid reflux and it worked wonders.
Best of luck!