I hope this is in the right place..
Anyway, I've been wondering about whether or not long hair can affect your health, specificaly: headaches.

I get a lot of them, sometimes they're just small and slightly annoying, other times all I can do is lay down and wait them out while it feels like someone hit me from behind. I get them often but irregularly and have for quite a while. I've been trying to figure out why.

My boyfriend has no ideas to offer but admits it does worry him, my father tells me that some people just get a lot of headaches for no reason. I've talked to friends and people I know and I've gotten a lot of reasons. Like, "it's your rabbit, it's his fur, get rid of him" or "you spend too much time reading you just need to stop for a while."
-but the most popular theory is this: "It's your hair. It's too long, that's what gives you the headaches."

I'm curious, can that really be the cause? I've heard of it happening to people with long hair before, and if it is the cause would there be any way to cure the problem while keeping my hair? Has this ever happened to you?

I'm glad you asked that Bardic Love. I've always come across a lot of people that seem to have that pre-conceived notion that long hair causes headaches.

It always kinda irritated me because I couldn't figure out why, if that were true, people in the 'olden times' wore their hair super long and didn't have any complaints.

When I was young I went to school with a girl with thick hair to her waist. She used to always get headaches and her mum kept telling her to cut her hair because that was the source. Eventually she caved and did, cutting it to her chin.

She still got headaches though. Turns out it wasn't the hair at all. She had scoliosis.

Then there is the case of me. I decided to get the 'brilliant' idea to put braided extensions in my hair when I was 16. I got a friend to do it. By the end of the day I was thrilled I suddenly had hair from above my chin to my waist. I also had a splitting headache. But that wasn't because of the length. It was because my friend had put the braids in too bloody tight.

I think what Bikerbraid suggests is very good though. I suppose it depends on how sensitive your scalp is and how thick your hair is. Perhaps it's possible to get them from your hair, but I don't think it is somehow.

Has anyone else ever heard of this?

Headaches can have a multitude of causes.  I had one for two days earlier this week and realized it was because I was "splinting" my jaw from recent gum surgery .  Once I began to relax that, the headache went away.
I think many headaches are caused by poor posture - yup, yup, just like Mom used to say   But so many of us spend hours hunched over computers or reading or other types of desk work we really stress out our necks and that causes headaches!
I agree tight hairstyles can do it too, or at least aggravate the problem. 
Lots of variables here...have to take a serious look at what you're doing (or not doing) when you get one.