Not sure how much this will help but when I got my positive on the FRER test I went to my docs and got a blood test (I was roughly 4.5weeks) the HCG levels were 18 and my doctor said that was barely a positive and that they should be much higher although I went on to have a daughter 8 months later!
Try not to stress, easier said than done I know, but only time will tell and unfortunately there is little you can do at the moment.
I also had a dull feeling in my lower stomach early in my pregnancy, I wouldn't have called it an ache or pain it was more just like a solid feeling in my tummy - if this is what your feeling then I'm pretty sure it's normal