Troubleshooting: Sourdough starter is not doubling
I've been interested in making my own bread for a while now. I finally decided to try and make my own yeast rather than buy one. This starter began on Tuesday, Sept 17th. The first week of this starter was in the 70s and 80s, but now this week we've dropped to 60s during the day. When it gets that cold, I leave the starter in the microwave for more insulation. The flour I use is whole wheat and was milled sometime in March of this year. I do weigh everything and tend to follow a ratio of 1:1:1, although 1:2:2 will probably be what I will start following. I feed every twelve hours.
Here's a summary of how it has been doing:
Day 1: Some minor bubbling, good signs.
Day 2: Explosion of activity, definitely doubled in size and overflowed out of the jar.
Days 3-5: Bad bacteria settled in; little to no rise with an awful smell (I know this is normal). Started feeding every twelve hours.
Day 6: Smell was fine, marginal rise.
Day 7-9: Consistently rising a quarter to a third up, but will move no further. Smell is yeasty and good through most of the rise but has a sharp vinegar smell and a thin layer of hooch closer to the next feeding time.
Day 10 (today): It was really cold last night, so I left it for the day to keep rising. Similar activity to days 7-9.
I know this starter won't be fully mature for a while now but I want to make sure there are no issues with it. If there are, I'd like to correct them. I'm only worried since most resources I've seen say that by now, it should be doubling in size.