Dear Tom,
I'am sorry to hear that your English isn't well..And I'd love to give you some advice on English learning.First,you should take it easy,so you won't feel you are under too much pressure any more.Second,you shouldn't study too late because that's bad for your health.And that's also why you have headache and stomachache.Next,you should often practice your spoken English by having English conversations with your friends.Listen to English songs and watch English movies can also help you with your English learning.
At last,I hope that you can improve your English soon.
Sincerely,
XXX