There is know way of knowing exactly what is wrong with you without doing examination and knowing your medical history. The area that you describe having pain is where the spleen is located. If you have tenderness in the area or pain anywhere else then please let me know. Your doctor will examine you for exact point of tendeness.
Do you have any other health problems? Are you taking any medications?
Left upper quadrant pain that you describe can be due to colon problems or problems with the spleen. Upon examination and testing it will be determined if you have an enlarged spleen or infection. Diseases of the colon can include anything from irritable bowel syndrome to colon cancer.
Let me know if you have any other significant symptoms, pain with eating, bowel problems etc.
Medical investigation is in your best interest at this time.
I hope all will be well with you!