White coating on the tongue during pregnancy is actually something a few of my friends experienced in their first trimester, and the taste changes you're describing sound like it could be related to hormonal shifts. That said, since it's not scraping off easily and you're not sure if it's thrush or something else, it's worth bringing it up with your gynae or PD at your next visit, just to be safe. They can take a proper look and rule out oral thrush or any other cause, rather than you worrying and guessing based on Google lah. Better to get a proper answer so you can manage it the right way through your pregnancy.