minimal spotting can occur in early pregnancy
due to many causes, journey is one of them,
as there will be increased blood supply to local organs because of journey friction can occur leading to minimal spotting, this will usually subside soon,
by taking protogest the bleeding will subside, recurrence can be prevented, if there is any premature uterine contraction because of journey that will also subside,
so there is nothing wrong in using the tablets for few days as prescribed by your doctor.