What is a healthy mile per day increase? I fear injury and im a new runner.

I've been running for like a month. I run everyday. When I started running I ran like 1.5 miles a day. Now I run twice a day for about 3 miles each run. Give or take .5 miles. Is this a healthy rate of increase or am I prone to injury? Thanks for the help Edit: I would like to run about 42 miles a week or more. I currently run closer to 30. How fast can I get to the target 6 miles EVERYDAY. I usually take one or two easy run days where I only run like 2 two mile runs.