Well, have you ever seen a girl with blush ALL OVER her face and neck? Sorry, no good excuse! Especially since you don’t wear the “blush” all the time – it comes suddenly.
When my self esteem was terribly low, I blushed for the dumbest things. I mean, REALLY blushed. Even if I just raised my hand in class. B”H, now, I rarely blush (although it’s more often than others). Good luck!