You clearly pulled a muscle or tendon when not carrying things correctly. You are doing the right thing with regard to walking. You can apply heat or cold, to the back, whichever one helps you the most. I usually find heat works better for me. You may benefit with having a massage with pain relief get that you can buy from the pharmacy or large supermarkets.
With regard to your head pains and feeling hungry, this is likely to do with stress and anxiety. You lost your job, having had to move, and are going to have an exam to do tomorrow. The anxiety can also make you not able to sleep due to thinking about things.
It may be head cold or a sinus infection that is beginning. For help to relieve this, you can do steam inhalations.
To do a steam inhalation, boil up a kettleful of water and pour this into a bowl (taking care not to get scalded). Put some Vick, or Olbas oil, or a few drops of any menthol type oil that you have (not cooking or olive oil). Bend your head over the bowl and cover your head and the bowl with a towel. Breathe in the steam through your nose and out through your mouth for a duration of 10 minutes. Do this 4 times a day, but any time is better than non.
Take pain relief for your headaches as directed on the packet.
If you symptoms persist for a few days without any signs of getting better, or get worse, make an appointment to see your doctor.
Make sure that you drink plenty of fluids (not alcohol) so that you do not get dehydrated. 2 litres a day is usually recommended, but you may need to drink more if you sweat a lot.
Please realize that i am NOT a nurse or doctor, but, there are several things that be going on. Your back could be a pulled muscle or pitched nerve due to lifting the wrong way or just sleeping in the wrong position for a long period of time. If the problem persist you might want to get your doctor to check you out. Your head and hunger issues could be due to stress, depression, exesive worrying exc. Or a completley different issue. Best advice is to go see your doctor. Make an appointment and get checked out. Make sure the doctor knows all and any otc and px drugs, symptoms, and what you have tried to help get the issues to go away. See your doctor soon. My apologies i can not be of anymore help.