It sounds as if you either have a Stye or a Chalazion on your left eyelid. Styes and chalazions are both caused by the clogging and inflammation of the sebaceous glands that line the inside surface of the eyelid. Styes resemble a pimple and are painful, usually self limited to 1-2 weeks, resolve spontaneously, and cause no residual damage. Chalazions, on the other hand, have a gradual onset, are nontender, take months to years to resolve, and also heal without any residual damage. From your information, it doesn’t appear that you have an infected stye/chalazion, and it doesn’t appear that you have a large mass. Therefore, home treatment with hot compresses for 20 minutes 3-5 times a day is the best treatment. If pain becomes worse, your eye becomes red, your eye or eyelid becomes swollen, or you develop blurring vision, go to your primary care doctor immediately for an evaluation.