Hi, it sounds like you have anxiety as you get stressed out over minor ailments and you think of some serious diseases which might not be the case at all. Firstly, I would suggest you to stop searching on the internet and go to an actual licensed physician for checkups. Please don't be offended but you are not a qualified doctor and diagnosing is not your ability or job. Secondly, for certain difficulties like headaches try taking crocin and if it still continues go to a physician because its also possible that you could have spectacles. I understand you wish to get into army and you still can but its also better to accept that you are only human and you will always have some medical difficulties. Visiting a physician will help curb your anxiety and also make you feel better rather than assuming the worst.