Sometimes you body can get used to certain medications and then the meds stop working, same for your hair, a shampoo can work really well but your hair and scalp get used to it and it doesn't work so well anymore.
I would try a different shampoo.
As for the dryness I would go to whoever cuts your hair or a beauty school and get a conditioning treatment. Where they condition your hair and put your under the blow dryer and it feels amazing<3 sometimes your hair just needs an extra boost.