I often take tea empty stomach and also take after meals sometimes. Are these habits unhealthy?

Well, I strongly recommend that you must get rid of this habit if you want to be healthy going forward. Let me tell you why. Because tea leaves are acidic and affect the digestion process when you take it after any meal. 

The whole scenario worsens if you consume protein in the meal, the acid from the tea hardens the protein content and makes digestion difficult. Drinking tea immediately after a meal will also interfere with iron absorption by the body.

Moral of the Story: No tea one hour before and after meals.