Problems with rear brake light and rear turn signal

A few days ago I noticed that my left rear brake light, left rear turn signal, and center high mount stop lamp weren't working.

So I went to the store and bought the appropriate bulbs. I replaced them all and only the center high mount stop lamp worked.

What's weird is that my tail light (which is the same as the rear brake light) works, but it won't increase the light intensity when I push the brake pedal... and the turn signal still doesn't work even with a new bulb.

What could be the problem?

Thanks in advance.