Brown blood & 'hip' pain

[mummyyessy]

I would really appreciate any advice here...

I have had some quite bad pain (on & off / twinges) in my left 'hip' area for about a week now. It's starting to improve, but today I've had some 'old' (brown) blood on a panty liner - not much, maybe 1-2 teaspoons. But certainly odd & completely in between periods. I'm otherwise pretty regular periods wise.

I'm 37, and otherwise well - if pretty overweight.

Until the bleeding today I'd sort of assumed I'd hurt my lower back / left hip joint...but the blood is making me thing it's more sinister...

I'm obviously worried it's something related to my reproductive system...or a mass / cancer, 

Any advice welcome. Thanks.