Abdominal pain on your left side is probably an indication of some problem with your stomach or the lower colon. You seem to be using stomach in the colloquial sense, meaning abdomen — and since you haven't specified whether the pain is in the lower left or upper left, it is difficult to say whether your stomach or colon is affected. However, since you seem to experience pain immediately after meals, the problem is most likely with your stomach itself. It is unlikely that your colon would show any reaction within such a short time after a meal.
One of the most common stomach ailments is a peptic ulcer. The causes of peptic ulcers are many, including bacterial infections, smoking, certain medications such as non-steroidal anti-inflammatory drugs or NSAIDs, and stress. However, it is not possible to be certain that this is the cause of your stomach pain without a full physical examination. Even if this is in fact a peptic ulcer, the method of treatment will vary depending upon the cause. Antacids will most probably be needed, but if there is a bacterial infection that is severe, antibiotics may also be necessary. You should therefore visit your family doctor for a check up, and only then begin any medication.
answered by G M