Life without qualifications so depressing and bad?

well im on my gcse's and done couple of exams already but now i am feeling more depressed. I was pretty positive on 1 of the exams out of like 5 so far. Now im revising maths questions and it is so hard. I pay attention in class but why cannot i not do it. When i do a topic in class i remember it perfect for a couple of days then i completely forget how to do it. What shall i do? I live in UK but i want to work in hong knog when i am older!!! i am so unhappy and really dont know what life will be like after gcse's. People can say go to college but my brother goes a rubbish uni after he graduated at college but he says that you cant get a good job if you go to college and that college is just for dropouts/people who are thinking they are getting something out of it. I am so unhappy and really i really wish i could have a normal decent life when im older.