[KJS]

Its not really clear in your intial statement if you specifically asked the dealership do an alignment and/or balancing recently? who did the rotation in February?
If the dealership/service department did all the above in February there's a good chance that something happened since then (or they will say you hit a curb or pothole, etc.) otherwise they would have sold you at least a new set of tires back then. And they are certainly not going to pay for a new tire or set. They will say something happened in the 6 months you were driving the car.
If you noticed something not normal after they did the work, you probably should have gone back to them right away.
BUT that being said you should certainly try to get them to do something for you. If you don't ask, its an automatic NO....