It seems like you have not had the right food or even not eaten at all.
Please make sure you eat right and also you eat on time and eat sufficient food. All your symptoms seem to be related to inadequate food intake except the diarrhoea
Take plenty of fruit juices as well. You will feel fine soon.
With regards to your girlfriend, speak to her and get things sorted out so that you can concentrate well on your studies.
You do not need medications for your current problems.
I wish you good health.
Take care and make the most of your life now.