brake lights out, directionals work sometimes

Hi, I have a 98' Chevy Lumina with 111,000 miles on it. Recently someone told me my brake lights were out on both sides. (top one works fine). I have also noticed my turn lights have not been working properly. Sometimes they will come on, other times they blink really fast (on the inside) and other times nothing happens at all. The brake lights and the turn indicater are all on the same bulb. I tried replacing both bulbs and nothing changed.

I started thinking it was probably the "flasher" but some have told me that if it was, the brake light shouldn't be affected.

Any ideas what the problem could be?

Thanks in advance if anyone can help me out.

Dave