Hey ladies, can anyone give me both fact based and personal based experiences on how soon pregnancy symptoms can show?

My husband and I have been TTC and right now I’m craving donuts (which I usually get sick over and hate...) and I’m insanely nauseas, peeing every 5 seconds it seems and more tired than usual. BUT it’s only been 3 weeks since my last period so I feel this would be insanely soon to show signs? Also I am correct in thinking that the best time to test is a few days after a missed period right? 😊 TIA.