Questions about pregnancy?

Okay, what are some of the earliest signs of being pregnant? When someone says I have to constantly use the bathroom, like its heavy on my bladder, what exactly does that feel like? Can having lower back discomfort be a sign, stomach hurting after eating something? Can taste buds become different? Like can lemon start to have a funny taste in your mouth? What about constipation, sleeping more often, feeling drained, sick after intercourse? Etc...