Milk supply help!

Not sure if this can happen or what is actually happening but I feel like my milk supply dropped drastically just in one day. I used to be able to pump 6 oz in one sitting and this morning I pumped 4oz and tonight only 1.5 oz. Baby boy has been super fussy today and was very stuffy and congested (we are visiting family in a smoggy area and was staying in a house with cats) we left that house to stay at another family members to help clear his congestion. Long story short not sure what’s going on with my milk supply..