I feel a bit under the weather.
I'm not feeling very well. / I don't feel very well.
I'm not feeling a hundred percent.
I think I'm going down with a cold. I've got a sore throat.
(Other cold symptoms are a runny nose, or feeling a bit "achy".)
我想我要感冒了。我喉咙痛。（其他的感冒症状：流鼻涕/a runny nose，感觉有点疼痛/feeling a bit "achy"。）
I've got a slight headache.
Other parts of your body which you can combine with "ache": toothache, stomachache and backache.
For all other parts of your body, say "I've got a pain in…"
如果是除了上面的身体部位，就用“I've got a pain in…”表达。
I'm not sleeping very well at the moment.
I feel a little faint.
I feel a bit dizzy. (when your head is spinning)
当你感觉眼前的事物在旋转时，用“I feel a bit dizzy.”表示头晕。
I've got a nagging pain in my shoulder. (nagging = a pain that won't go away)
I've got a splitting headache – I hope it's not a migraine.
注意：动词“feel”可以用在现在时和现在进行时中来表示你现在的健康问题。现在进行时更多的是暗示暂时的感觉，但是现在时和现在进行时的差别不是很大，比如"I don't feel very well" = "I'm not feeling very well."
I'm sorry to hear that.
Actually, you don't look very well.
You look a little pale.
Maybe you're going down with something. There's a bug going around.
Maybe you should go home and get some rest.
Why don't you go home and have a lie-down.
Is there anything I can do?
Shall I get you an aspirin?