My one eye small and one big?

Yes and NO : The two sides of one's body are not totally symmetrical, so it is not unusual to have a side bigger than the other. However, there are illnesses that are associated with a change in size of the eye opening or swelling..Etc. So it is best if you see your doctor for a proper evaluation to decide if this is normal for you or it is caused by an ailment.

Eye difference: Differences in the sizes of the eyes if often due to a difference in the lid position and the eyes are actually the same size. Rarely, the eyes can actually be different in size. See an eye doctor for further evaluation. If the appearance is due to lid position, it can be surgical corrected.