I would recommend that you go to see your primary care doctor
about this as soon as possible! The symptoms you have are a bit vague and, if they have all started together at about the same time, then I think the most likely possibility is that you are experiencing some viral illness, such as the flu or a stomach bug. Typically a viral illness leads to vague symptoms, such as aches and pain, nausea, diarrhea
, and the like.
Additionally, if you have had significant diarrhea and nausea, you may not have been taking in adequate liquids, and you might be dehydrated. Dehydration could be causing the symptom you have of lightheadedness and headache
Your doctor will be able to perform a thorough examination and help figure out whether this is a virus, whether your are dehydration, or whether you have something more serious going on.
Depending on what they find, they will also be able to recommend treatment options, which might include medications for nausea or diarrhea. While you are waiting to see your doctor, make sure to take in as many liquids as possible!
Please see your doctor soon, and I feel better!