What do these symptoms mean?

you could have developed intolerance to milk. You could also have a bacterial infection of the bowel. You are tired, feeling weak and have a headache because your body isn't getting the nutrition it needs and is loosing electrolytes with the diarrhea. If this has been going on for a few days I would go see the doc. Try not eating or drinking anything for 4 hours. Start out with clear liquids (koolaid,soft drinks, tea,broth half strength juice,jello, clear popsicles) in small amounts at first, half to a cup every half hour or so. If these seem to do okay go to cloudy liquids ( pudding, cream soups.ice cream, egg drop soup.) Okay here is where I need to say that if you are milk intolerant you will quickly feel the cramps and stomach pain. But, do not be surprised if you feel some aching anyway your system has been through the ringer. From there go to things like chicken noodle soup, noodles (no tomato sauces yet), toast, crackers. Then try things like scrambled eggs, mei fun, lo mien, moo goo gai pan, pot pie,baked or mashed potatoes. Go slowly and do not stuff yourself. Keep up the fluids. Good luck.