I didn't get a 1099. Do I owe tax?
Yes - All money or items of value (barter or trade) you receive for selling merchandise and providing services is taxable whether or not you receive a 1099.
It's your customer's responsibility to file 1099s. If they don't, that's their problem. You still must report the income. And there's no minimal amount.
Also read Who should get a 1099?