Why are my eyes two different sizes? (Photo)

I noticed that my eyes are two different sizes. I noticed this problem waking up in the morning. It becomes obvious in the morning that one eye is bigger , sometimes red in the morning. Let me tell you how I sleep maybe this can help, I sleep on my soltomach and half my face is squashed in the pillow so I use one eye when using my phone. Sometime I find myself closing one eye (the one in pillow). The redness in the morning is in the eye I use in bedtime. It is the smaller eye in picture.