Is this normal? Been on birth control for 9 months. Forgot a pill. Doubled up the next day, but started bleeding. I figured it was breakthrough bleeding. Have had brown discharge the past 3 days following. Is this normal? Now it's turned back into blood,

Likely not. Most women who take birth control pills have no side effects, but the most common side effect in the first 1-3 months is irregular bleeding that gets better over time. Missed pills can also cause breakthrough bleeding. There's little evidence that 1 pill is more or less likely to cause breakthrough. Most people who take within 1-2 hrs don't have breakthrough. I'd suggest continuing to take pills.
That . That is unusual given that you just missed one pill. It is appropriate that you took two the next day. Observe your bleeding pattern and if it doesn't resolve over the next few days then please be evaluated. If you are at all concerned about infection then please be checked, although the discharge sounds more like it might have been spotting. Your symptoms should resolve but if not then please be evaluated.