What Causes Nausea Even After Taking Normal Food?

Very confused. Completely normal foods will sometimes give me a short wave of nausea that quickly resolves, or make me spontaneously heave, or even spontaneously throw up if I can't control it. I can no longer eat avocado as even a small amount will make me throw up. I won't feel sick before the episode, and I feel completely fine after. Sometimes bananas make me nauseous for a moment, but just now, one bite caused me to heave. Eggs are also a common food that will give me a nausea wave and I'll just stop eating. I am 28, 155 lbs and 5 foot 5 inches. I don't know what's going on and with exception of avocado, all these foods are hit or miss. I never know when it will happen.