I totally agree with Brittny...
It took me about 5 months to get regular after my mc last year. The month after I had my mc, I got my period normal...then it took 45 days the next cycle, then it took like 28, then it took like 32, then it went to 28...It was a roller coaster! My doctor said it was completely normal though. Hang in there and call your doctor for reassurance.
Remember that your cycle might not normalize right away after your m/c. With me it took 45 days to get my first cycle and shorter every cycle after. It took me 6 cycles before I was back to 28 days.
If you are worried that you are pregnant again I would call your Dr and get a blood test done to see where your levels are at. I wouldn't want to take an HPT and come out positive giving you false hope because you still have HCG from your m/c in your system.
Good luck and let us know the outcome
The worry for me in answering this question is do you still have hcg in your system from the miscarriage? If yor levels were checked and your hcg level is back to zero, then you can test the day after your period is due.