I need advice cause i cant afford medical help.?

Ive been having severe lower back pain for a while now.I don't know the cause of it but its getting worse. Everytime I cough I almost collapse to the floor, sneezing and laughing to hard do the same. I've just very recently had to quit smoking, and i'm slightly overweight but i don't get out much or do much strenuous activity, i cant afford a chiropractor and when i crack my back, it still doesnt go away. i don't know if this is a pelvic infection or chronic back pain, but i would like to know what it is or the causes of it, cause its affecting my everyday life. and to mention, i'm only a 20 year old female.