Thyroid disorders don't commonly cause a slow moustache growth. Even if thyroid is a cause, moustache should be normal once you start taking thyroid meds. In most cases, it is genetically determined, and external treatments are mildly beneficial at best, if at all.
Need to take a proper history and examination to look for possible causes.
Next Steps
Consult a General Physician / Dermatologist.
Health Tips
Avoid falling for unproven products sold in the market. This could delay the actual management.