the HCG levels will take sometime to reach zero, that will depend on the gestational age
when abortion occurred, so that may be cause for your positive pregnancy
test and also after abortion ovulation has to recur for periods to occur and the time when it will recur varies,
in case of procedure like D&C for abortion there is a chance for pelvic inflammatory disease
which can cause pelvic pain
, rectal pain could be because of that or due to hemorrhoids.
so if your problem continues better to consult gynecologist once and get examined to find out the possible cause.