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If you have a history of an ectopic pregnancy
and having no sac in utero with positive blood tests , there can be a possibility of an ectopic pregnancy this time also.
Sometimes the sac is not visible due to an early pregnancy.
Pain can be due to previous surgery or fresh ectopic .
Repeat an ultrasound
, TVS scan would be better.
Consult your OBGYN
as soon as possible.