17:43:52: Audio Format: 48000 Hz
17:43:52: ------------------------------------------
17:43:52: Audio Channels: 2 Ch
17:43:52: Playback device {0.0.0.00000000}.{01ba8c74-89a1-4e44-bcfa-1a97f5ee69c3}
17:43:52: ------------------------------------------
17:43:52: Using desktop audio input: Speakers (Turtle Beach P12)
17:43:52: Global Audio time adjust: 0
17:43:52: ------------------------------------------
17:43:52: Audio Encoding: AAC
17:43:52: bitrate: 320
17:43:52: Using Monitor Capture
You don't have a microphone device set in that log at all.
320kbps is MASSIVE overkill for AAC. At absolute most you might use 160, but 96 or 128 is more than enough.
Don't use Monitor Capture, use a Game Capture on the Isaac process.
Check your mic's audio levels in the recording devices->Properties section. Make sure it's not set super-low, and that Mic Boost is on (if applicable).
Check your OBS settings. Ensure it's selected as your mic. After that, you can use a mic multiplier to boost your audio within the program.
Have you tested the mic with Skype or similar? Might have just gotten a bad one, failing all else.