mazda3 HELP

I have a 2008 mazda3 hatchback which I was told has a bad sensor and my car is "messing up in a good way for me" the temperature gauge inside my car goes all the way up to H but my car is not actually hot. The engine light has came on for this. BUT today when I got home from downtown my car was making a bubbling sound and almost all my coolant is gone, what do I do!!!!!!!!!! some one help me :(