hi - my 12 week old is also on 3hour routine, although in the last week i have started to relax a bit on the clock watching and am finding that sometimes she wants to eat more frequently in the afternoon - so i let her! This is also helping my milk supply (which I was also concerned about). I have also started expressing around 2pm to ensure that the supply is more even - you could try that - even 5-10 mins of pumping each day will boost your supply.
I also have been having the one sided problem intermittently. The bf counsellor says it could be that she just wants a drink and so if one side is too 'foody' rather than a drink she is refusing - i used to think she was full, but then i try her on the opposite side and she is often happy to keep going. The other suggestion they made was that she may have a stiffness in her neck, or i may have a blocked duct or slow let down on that side and she is impatient... so now i squeeze some out before i start feeding to check its all working!
re sleep.. i have always been on three hour and been lucky that my LO usually only wakes for 1 feed a night. this moves around the clock, and sometimes none at all (last night!) I definatley think that its related to the days feeding pattern.. i do three hour till the first afternoon feed and then after that watch her cues and am findning that she is telling me she wants more, more often. Apparently they know when afternoon strikes that they are in the rundown to night time and so will want to take in more calories to get thru the night.. in my humble opinion i think this makes sense and she is happier at bedtime. why not stick to 3 hour easy till 3 ish and then go on to 2 or 2.5hr.. better still watch her cues and see what she wants.
my naps have also recently changed - they were getting very bitty (40 mins etc), so for three days I stopped EASY, fed when she wanted and watched for naps - i refused to look at the clock (it was so weird!) and when she was tired but wouldnt sleep i took her out in the car (would have used anything guarenteed to make her sleep). This gave her the longer sleep she needed, but more importantly broke the cycle she was in - now she has gone back to 1.5 hours or an hour some afternoons, but she is not overtired - i think she is just able to stay awake longer now.
final thought (sorry to ramble).. I personally dont agree with Gina Ford's method, but i recently read her routine for a 12 week old. Naps are only 3 hours ish a day and I cant rem if the feeds were three or four hours, but the interesting thing was that come the afternoon, the feeds were more clustered and back to 2 - 21/2 hours... seems the general opinion is to start tanking by the afternoon...hope this helps