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How old are you?
Does this worsen with standing up?
Do you have any heart issues?
This could be related to an issue known as "pre-syncope":
and in older people, this often can be heart rhythm related.
In a young person, this could be related to anxiety, or dehydration (which may lower your blood pressure), illness, medication reactions.
It's hard to correlate the lightheadedness with the pinching pain in the stomach, but certainly if you aren't feeling well, you could have more of these types of symptoms.
At 18, a heart rhythm issue isn't going to be likely, but should you continue to feel lightheaded (and are well hydrated) -- then speaking with your family doctor would be helpful.
If you can test your blood pressure during these episodes of lightheadedness, that also would be helpful for your doctor to evaluate.
Perhaps discussing this with your doctor would be a good idea, to get your blood pressure/heart checked out.
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