If you have a hard time memorizing things, it is wise to try not to learn too many new things at the same time. Wait until you have fully memorized a piece of information before moving on to the other. Learning many things at the same time will just make everything scramble in your brain.
You should try to socialize and have fun. Although it sounds strange, socializing with friends is a great workout for your brain. Laughing is also vital for brain health, as it uses many parts of your brain. It can also help you to think in broader terms and keep it active.
Try meditating. Meditation can help you against anxiety, depression, and stress. Studies show that regular meditators have much more activity in the the left pre-frontal cortex. This special area of the brain is associated with feelings of joy and equanimity. This also allows the brain to make more connections with brain cells, increasing memory and mental sharpness.