I went and search the internet and found some possible causes for P0107:
1: EGR boost sensor malfunction
2: Open or short circuit between EGR boost sensor & PCM
3: PCM malfunction

Now what is a boost sensor? I've already made an appointment, but if I can resolve this by myself, it would save a lot of money. I'ts not the EGR itself because I just replace it, then drove it for a couple of miles.