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 are 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 not minimal amount.

Also read Who should get a 1099?