It is likely either or both - barring anything else. If you are curling your lashes after you put on mascara, then it's not surprising. That's a taboo. But sometimes it's just the mascara itself - it depends how much you use of it. The more you put on, the more brittle your lashes get; the more brittle, the more prone to breakage. Naturally, this isn't a rule - it could simply be a phase your lashes are going thru. As for the curler, that is better left away from your lashes - they are notorious.
They have this stuff called Talika eyelash gel that is supposed to promote (re)growth. I've not tried it (although I'm really tempted to!)...but I heard raves about it from a lot of people. It's expensive (but that's relative, isn't it).
Anyone out there with experience with Talika? Would it possibly help?