Listen, building a character is incredibly fun and rewarding. Never forget that. But DnD is a time consuming hobby, that requires a lot of time and often a lot of creativity. This is no excuse to make things easy on yourself, but if you're low on time or struggling with inspiration, here are some backstories for your character you can use.
Bard grew up in a difficult household. Their parents loved them but they struggled with addiction and poverty, and so Bard often ended up absorbing the brunt of their anger. They transformed that sad home life into jokes and comedy, going to great lengths in order to get a laugh from their fellow kids and other adults. As they grew older their skill in comedy grew, and in a world where laughs are so few and so small, their routine was a delight. Bard didn't realize they could turn a profit with their silly act until a band of travellers passed through town, and after hearing about the young comedian offered them a respectable amount of coin for a performance. They accepted and the travellers loved the routine. One of them, a musician searching for a legendary instrument, approached Bard after offered to pay for their entrance to a local bardic college. Supposedly the school had gotten boring, and a new style of performance would do them good. In addition, Bard's delivery was solid but their material needed some expanding, there's only so many jokes one can think of when stuck in a small town. Bard said yes on the spot, packed a small bag and left that night to go learn more about performing, and to see the wide world. In order to make jokes about it.
Paladin grew up extremely religious. Raised from a very young age by parents who had found their religion late in life, Paladin was never exposed very heavily to the outside world. They were sheltered and schooled at home, most of their teachings involving their family's god. Their parents were sure Paladin was destined to be a holy crusader, and told Paladin so for as long as they can remember. But a holy crusader cannot crusade if they never leave the house. Paladin's parents threw a huge party, though Paladin didn't have many friends that attended, as they bestowed their very own weapons and armor that they were using during their own religious revelations. With that, Paladin's parents sent them off into the wide world. Paladin is sure they're destined to become a hero of their holy order, but other than following the words of their god (which in general are incredibly peaceful), Paladin isn't entirely sure what to do with themselves. So now they wander the countryside looking for signs from above telling them what it is exactly they're supposed to do.
Wizard studied diligently for years, and years, and came to the realization that the whole world must be a storybook. Either that or some strange form of magically encoded mechanical machine that operates without the need for maintenance. One of their theories is that the conscious races of the world are actually the maintenance workers, without even knowing it. Wizard seeks to prove this point, and believes the way to do so is by figuring out just what exactly the conscious races are actually accomplishing, or rather what do they do accidentally in their quest to accomplish whatever it is that a conscious creature is attempting to do. Wizard figures that the most historically noteworthy folks are the ones that must be doing the most maintenance, and figures they'll take up with whoever seems to be the most historically noteworthy. Wizard's colleagues, and they've had a large number throughout the years, are divided on whether wizard is a genius or not. Some claim that Wizard's logic is solid, so long as they can return with some evidence showing that the by-products of consciousness accomplish something. Others claim that it doesn't matter at all whether the world is a storybook or some kind of magical machine, because consciousness exists regardless of the reason. Wizard ignores most of the thoughts of their colleagues. All they're looking for is proof.