Why am I experiencing nausea and headache after eating food?

Hi XXXXXX,
Welcome to XXXXXXX forum.

With the available described details, there could also be possibility of acute bacterial gastroenteritis.
Presence of nausea, frequent urge to use washroom suggests the diagnosis.

You should consult with XXXXXXX medicine specialist/ gastroenterologist and should go for thorough check up.
She should also go for complete blood count, ultrasound imaging, and serum electrolytes, renal function test.
She should take complete antibiotic therapy, antispasmodics, probiotics, antipyretics, if needed.
She should also take analgesics along with muscle relaxants.
She should maintain your hydration status by taking potassium XXXXXXX liquids.
Frequent loose diarrhea may cause loss of potassium with weakness and fatigue feeling.
Take soft diet along with yogurt and banana.
Avoid milk and all milk related products.

Hope that helps.
Let me know your other query.
Take care,
Dr. Mayank Bhargava