Ford Fiesta ST215 braking problems! Help!

Hi guys, I'm new to this fourm so hello all! I have a frozen white mountuned fiesta ST 2015.

i have a problem with my brakes as they seem to be very weak and they squeak constantly when driving after 5 mins or so. Couple weeks ago I was driving with very hard braking I ended up finishing all my pads so it was metal on metal. I drove about 15/20 miles with the front discs having basically no pads. I got my pads changed (brembo) but after a day or so of driving, my right front disc started to squeak as I drive and then the squeak would stop when I brake. Gave it some time as I thought it could just be the pads trying to wear in. After some days of driving and occainally some hard driving it didn't stop so I ended up buying new discs (MTEC DRILLED & GROOVED), had them fitting to my car and my brake pedal was very loose after I drove away from the garage! After days of letting the pads wear onto the discs ( which what the garage said to do) it was still very loose and very weak braking. The garage then had a look at my pads and there was a crack between the metal holder of the pads and the actually pad material its self which they said would seem to be a manufactory fault. I then got new (Pagid) pads which made the pedal and car stop a lot better but are still very weak compared to how they used to do! The pedal still goes slightly lower then before all this problems. It also doesn't stop well but the constant squeaking has stopped on the front right disc and has now moved to the front left disc!! It has been constantly squeaking from 2 weeks now as the garage said to just jet the brakes down with water when they are cold. The squeak stops for a few minutes then starts again! Also when I brake at high speeds, the car starts to vibrate and I feel it on the pedal. 

Sorry for the eassy but in need of help badly!!

thank you in advance.