Will my milk supply increase again if I have noticed it dropping?

Yes. Sure, if we know what caused the drop in supply. Breastmilk is made on a "demand and supply" schedule- the more milk out, the more milk is made. If you haven't had as much milk out, for multiple reasons, your supply will drop. Feeding the baby more (more milk out) will help that drop. If you are still having problems, getting help from a lactation consultant is your next best step!
Yes. Often something contributes to decrease in milk supply - stress, illness, lack of sleep - that is transient. If your baby is young (less than 4 months) you are very likely to be able to increase your supply by resolving the stressor and by increasing expression of milk. As baby gets older, substantial decreases in supply are harder to resolve.