12 weeks, brown spotting, freaking out!

Lindsay
Im 12 weeks, 3 days with di/di twins. This morning I woke up to scant light brown spotting. No cramping, no red. Have done it a couple more times. Talked to my doctor and he said it's very common, to take it easy, and drink plenty of water. 
Has this happened to anyone else?  I know he said its common, but I had a miscarriage last year and I am totally freaking out.