Symptoms mean nothing in regards to pregnancy, and should be disregarded. You can have all of them and not be pregnant, and vise verse. You can have none and BE pregnant. You said you had a positive test, but decreasing levels. What were they monitored to? If they dropped to 0 (or at least under 5) then no, you would no longer be pregnant and the symptoms would either be created or caused by something else.
After a miscarriage, it can take upwards of 8 weeks before you get a normal cycle again. Some women do immediately after. It really just depends on the female in question.
How didi you find out? was it a hpt or a blood test?