why current flows from positive to negative charge?
Current does not flow FROM positive to negative charge, it IS a flow of the positive charges. This is a matter of convention which was chosen despite the fact that free charges in metal conductors are electrons, which have negative charge.
But, current does flow from HIGHER to LOWER potential. The electric field, and therefore force on positive charges, is directed away from the higher potential towards lower potential. So the free positve charges placed in electric field will naturally move towards the lower potential. This is analogous to any object falling down due to the force of gravity. It moves from the place with higher gravitational potential towards the place with lower gravitational potential.