My cockatiel has abnormal droppings.

[MossyBird]

Hi y’all. I’m honestly not sure what to do right now or if I’m posting in the right place so please forgive me if I posted in the wrong place but today my cockatiel, Tiki, started having yellow droppings. There is still the white part in them but they’re just not his usual green. I have recently switched his diet to a pellet, seed and veggie mix so perhaps that’s it? I’m not sure. It might be a parasite but I really hope it’s not that. I’ve called every avian vet within about 50 miles of me and all are booked until next month. I’m a minor and can’t drive without a licensed adult and my parents are far to busy to sit with me for 2 hours just to drive my bird to a vet. I love my bird so much and want him to feel better. He is acting normal besides the abnormal droppings. I’m just very anxious and don’t want him to just drop over night because of my mistakes. I’ve disinfected his cage and booked a check up appointment in april but i’m scared that it could be to late? Anyone with any advice? Am I just over reacting to this?
My bird is a 1 year old cockatiel, he turns 2 on april 1st. He’s my sweetest boy and I raised him since he was a little boy after his mother pushed him out. My family has a history of raising cockatiels but this is my first cockatiel and I’m still learning. We had one health scare once where he vomited once but then was fine the next day. I’m sorry for rambling, I just am worried.
Thank you for reading.

 

[sunnysmom]

Switching birds from seeds to pellets will often turn the color of the droppings from greenish to brownish. If you post a pic, we can maybe tell you more but I suspect that's what's happening if you say he's acting normally other than that. Also what vegetables is he eating?