I suggest seeing a naturopath. I had chronic issues after the birth of my first son and between my OB, my MD and my Endocrinologist (thyroid issue just in pregnancy) they couldn't figure it out. Within two visits to the Naturopath, I was on the right track! They take unbelievable health history, ask questions you never thought mattered and it's for a reason-they are looking at the whole you.
I too think it may be caused by something you are eating. They will be able to put you on and monitor you on an allergy elimination diet. You may have developed a food sensitivity to something that you have always had and this is how it is manifesting itself. You have had two children in the last 4 years and with each pregnancy, your body (and it's chemistry) can change.
At 29 years old I found out I had developed a food sensitivity to eggs-something I had eaten alot of my entire life and never had an issue with until after my first pregnancy, that food coloring made me temporarily "depressed" and that I am unable to properly digest meat proteins (pork and beef only) with out digestive enzymes.
It can be very expensive if your insurance doesn't cover, but if you explain your situation, alot of ND's will see you the minimum and schedule followups every few months or so depending on your health situation. They are worth every penny. Actually, I need to take my own advice and make an appt soon!
OOOO and one more thing, have you tried that old wives tale thing where you put vicks vapo rub on the bottoms of your feet when you get into bed and put on white socks? I swear I did it once and it worked (maybe psychosomatic??)