Oh, darling, I am so sorry to hear that. There are many possibilities which may cause hurt and irritation of your eyes. We know that tears tend to dry and leave a residue behind such as salt and dirt. If you rub your eyes when you are crying, they may go into your eyes and cause more sting. Are there any eyelashes in your eyes? They will lead to sting too. Or maybe you are just too tired after long time of crying. Don't cry any more. Everything will become better soon.
Take good care of yourself girl. I can understand your feelings. I just broke up with my boyfriend last week. But I haven't cried a lot. I focused my attention on my work and never let my mind go away from it. I often believe that out of thinking out of mind. I think your sting may caused by rubbing. If you rub your eyes when crying, you may rub in of dirt which will cause your sting. Maybe a few eye drops can help you to solve your problem.