I just recently purchased a cockatiel from a pet store. A few days after the purchase, I noticed that my bird would sound very congested, and at night, she would sneeze repeatedly. The sneezes sound very deep, as if it may be coming from the lower area of her lungs. Just yesterday, she appeared somewhat lethargic, and now her fecal matter is runny. I also noticed some very slight bobbing of her tail (almost imperceptible unless you observe her closely).
She's still eating well (she actually eats a lot), and her eyes clear and wide open.
I'm hesitant to take her to an avian vet as she's been extremely stressed from changing environments (from the store to our home) yet I'm not certain if this potential illness may progress into something worse. I appreciate any suggestions you may offer.