I have not a burning sensation but just a warm rush in my left upper stomach, this just started recently what could it be? it is not constant.

Gastritis : You may have mild inflammation of your stomach but I do not have enough information. Try an H2 blocker such as Zantac or an antacid such as Tums if it continues to bother you. If it persists you need to see a doctor and get a definitive diagnosis

Warm feeling: This rather vague symptom may be due to mild irritability of the superficial nerves in the abdominal muscles as it appears of and on with no associated digestive symptoms or relationship to meals. It's questionable whether it's worthwhile investigating this symptom at this time,but if it persists much longer, changes or worsens see a physician for evaluation.