Overwatering has something to do with the way the plant looks. Purple stem could mean lack of Nitrogen. I would get it in soil that doesnt have miracle grow in it. Mayble try Scotts. Should only water every few days so that the soil is moist not wet. Miracle Grow sucks. I almost killed my 5 plants using that shit. If you can get some good nutes. Foxfarm, general hydroponics are a few that people here use.
I would suggest moving the plant inside as well. Winter time is the budding time and like other people have said you arent going to get much outta that plant. Move it inside, get a good light on it, put it in good soil, get good nutes... and dont overwater. Good luck.