I know it happens to a lot of people, but I mean I cry for no reason even when people try to help me. Once I tripped and it hurt because I hit my knee pretty bad. I got sent to the nurse and so on but anyways she asked if I wanted to go home and if it really hurt, and I started to cry for NO REASON. She was trying to help but I couldn't resist. Also today I got lunch detention for some speed quiz thing we were doing, and I almost cried when my friend laughed at me and damn it was hard to hold back those tears, and the whole class laughed at me too and I almost cried at that point too. But the teacher ended up saying it's alright I don't have to stay, and I almost again cried of happiness but I was pissed off at him. I think I cry mostly when I'm put in a situation where I'm the center of attention in bad situations most of the time.
That could just be your personality. Some people are just sensitive, and you happen to be one of them. If you aren't, then it could be your age. I'm 13, and I cry all the time for what feels like no reason. My sister tells me she was the same way at 13, so I'm assuming that it's a phase. Yours is likely a phase, too.
Just let it out you do have a reason but you try to forget about it