You didn't mention your parity level.
If you are pregnant for the first time,
little amount of bleeding can occur during first weeks of pregnancy as,
1. gestational sac
is getting implanted in one wall of the uterus
and remaining cavity in which also decidual changes going on will be open to the cervical os,
2. because of burring of gestational sac into the wall of the uterus bleeding can occur which will present as little spotting,
3. Presence of sub chorionic hematoma
may present as spotting,
4. increased blood supply will be there to the cervix
during pregnancy. So, stressful work done by the woman,
or by traveling to longer distances in vehicles like bus, bike etc.
or participating in intercourse,
or any local injury
all these can cause spotting during pregnancy
. If the amount is little without pain no need to worry. As you are already on progesterone
and your doctor confirmed that your baby condition is good no need to worry but be careful and visit doctor if heavy bleeding with pain occurs.
In case of repeat pregnancy also above things apply and also if you had previous miscarriage
be little bit more careful and continue the medication, avoid the cause which led to previous miscarriage.