DD has gray tongue. Is this oral thrush?

Hi! I hope some of you can give me an idea of what to do. I’ve done google, webmd and other mommy group pages. I’ve noticed something different with my LO. I’m exclusively breastfeeding her since she was born. Last week this showed up. I’m shocked because it’s gray. She doesn’t have a diaper rash, no fever, it’s just exclusively on her tongue, not on the inner cheek, she’s very active when she’s awake, feeds very well too, whether it’s me nursing her or solids. I used to just see white before and we constantly rub them off after her bath. From the moment we saw that, we’ve tried rubbing if off with gauze and scrape it off with her toothbrush but it’s not working. She loves chewing on her toothbrush, but wit’s a struggle to try and scrape it off but we tried everyday. I hate that she cries whenever we are cleaning it. Breaks my heart. I read that thrush is commonly white, but this is gray. Also, my breast are not painful nor itchy. We used to give her Novoferrum (multivitamin with iron raspberry and grape flavor) at night, we shifted it to morning so if that’s the culprit for the staining in her tongue we’d have better chances of lessening the stain because she eats solids and nurses a lot around daytime. We just added yogurt to her diet so it could give her good bacteria. It’s a little thicker now even though we clean it everyday. Just can’t get a picture of it because she gets upset. Thinking of trying nyastatin or gentian violet. Has any one of you had this with your LO? I feel like I’m the only one with this problem. Will be contacting her doctor soon. Just want to have an idea if we can do something else to not let this get worse before we can get her an appointment.

Update: Showed this to her doctor with photos and videos. He said it’s nothing to be concerned about as long as DD is feeding/eating, pooping and acting normally. It has also been two weeks and it’s going away slowly. Thanks to everyone who responded. ☺️