I agree with shroom. You're having problems digesting your food. And if this has been going on for 5 months, you are at serious risk for many nutritional deficiencies, which will cause a million different symptoms for you.
This is just one vitamin, but if you're low in it, you'll have everything from trouble breathing, trouble digesting, and trouble thinking. You'll even eventually have nerve pain in the feet.
Take a digestive enzyme with every meal. And then take apple cider vinegar about 30 minutes after you eat (no sooner). This should help you digest your food.
If you're not already, take a strong b-vitamin. All the water soluble vitamins are the first to be lost when you have a problem like yours. This includes minerals too, like zinc and magnesium, which we need every day. So take a multivitamin - a good one. Plus extra b vitamins, c and magnesium.
As for what caused this... hard to say. Could be something you've been eating. Lots of raw fish? Do you eat a lot of sugar, drink tea, alcohol or coffee? Do you have a thyroid issue? Diabetes? Have you had an illness? Have you been taking any unusual supplements or herbs? ALA? Medications? There are many many things which can deplete us of vitamins, even things which are supposed to be good for us.
Regardless of the cause, these suggestions will absolutely help you feel better. If you find that you don't improve, then at least trying these suggestions will give your doctor more information to go on. There is a bacteria and a parasite which can suck vitamins out of you. But it's not the first thing to suspect, unless you eat a lot of undercooked meat or raw fish.