Why does my husband buy medicine and big data show my mobile phone number?

Maybe it's because the phone number registered when your husband bought medicine was yours.

Drugs controlled by the state need to be signed by prescription, and their identities need to be registered for easy control. Therefore, pharmacies need to register personal information such as ID cards and telephone numbers to buy medicines.

You need to see your ID card to register in a drugstore, but you only need to fill in a phone number, so your husband may have filled in your number by mistake.