Good morning doctor, I'm Sonita and I'm 4weeks...

what drug to take to avoid miscarriage?

well there is no drug that actually dedicate to avoid miscarriage, the only way to do it is by regular follow up in the clinic for early detection of the risk factors and early treatment of them , risk factors could be infection, anemia , drugs or medication , thrombophilia and others, some may recommend progesterone injections but this may be not scientifically proven.
medical diagnosis:

this can be done by regular follow up with each presentation, doctor will check vitals and make sure everything is going normally with pregnancy, and investigation may be required such as CBC, urine tests, and others could be requested according to the exam
Signs and symptoms:

if you develop the following you should be checked directly:
- bleeding
- excessive cramps
- discharge out of vagina
- rashes
- hypotension
- excessive vomiting
- severe headache
- others