Question: Microphone volume on recordings is low.How to fix this?

Answer:
Check that  both speakers are on the same level. By default the recording is stereo, your voices from the left speaker and the person you are talking with from the right.

MP3 Skype recorder is recording directly from audio devices. Hence the sound recorded as it is, no internal Skype volume adjustment are on recordings. You can try to increase volume of your mic in windows settings. Right click sound icon in system tray. Choose 'Recording devices'. Choose your mic from the list and click Properties button. On the new screen go to 'Levels' tab. Move microphone slider to the right, you can also try Microphone Boost slider setting.
Please also consider using  headset to avoid echo, the way radio shows avoiding echo on recordings.