I am sorry to hear that Diva is crying and straining to urinate. I think that she is definitely trying to get your attention and tell you she is uncomfortable.
Cats can have inflammation and discmfort due to an infection, crystals or calculi in their urinary tract, or even a mass in their urinary or reproductive tract.
Cats with sterile inflammation of the bladder (Interstitial Cystitis) can have an inflamed, thickened bladder lining that bleeds.
Cats tend to be poor drinkers and as such have very concentrated urine which can allow irritating crystals to form in her urine, which can lead to calculi forming.
It sounds like she straining to urinate, only passing a small amount and urinating frequently.
Is she licking her genital area more then usual?
Is she eating normally?
I know that a veterinary visit isn't inexpensive but this may be something that we can easily fix and if she is crying and straining that means she is likely uncomfortable and experiencing inflammation and urges to go.
I don't think this is an emergency tonight, but the sooner you can get her seen the better.
Being female (short urinary tract) an infection is very likely, and that we can help easily in most cases. I would start with a physical examination and urinalysis with culture to see if she has a health problem. Depending upon her examination findings radiographs and/or an ultrasound of her abdomen to evaluate her kidneys and bladder may be recommended.
It is possible that she has calculi (stones) in her bladder too, that may require surgery.
Worst case scenario is a kidney infection or a tumor in her bladder (very unlikely at her age).
You can choose how involved you prefer to get with diagnostics, but a urinalysis with culture is relatively inexpensive and usually is enough to get us started in helping her.
What you can do for her at home is encourage fluid intake to flush out her urinary tract. Add water or low salt beef or chicken broth to her food or feed her canned food with warm water added to encourage eating and increase her fluid intake. The more she drinks the less concentrated her urine will be and the less it burns. Flushing out her urinary tract is a great idea no matter the underlying cause.
Offer her fresh water, tuna juice and low salt broths to drink frequently.
Omega 3 fatty acids are natural anti-inflammatories. Though they may take several days, or even weeks, to help but they may be something you want to use for her long term, especially if this is a repeated problem for her. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your kitty's weight. I recommend an omega 3 fatty acid dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give her 20mg of EPA per pound of body weight per day. For example an 8 pound cat could take 160mg of EPA per day.
If your regular veterinarian is beyond your means financially now your other option is to contact your local shelter or humane society on Monday and see if they run a low cost clinic or know of one in your area.
If not here is a web-page that lists some that may be able to help:
Other sources of help can be found here: http://speakingforspot.com/?p=Financial%20Assistance%20for%20Veterinary%20Care
Best of luck with your girl, please let me know if you have any further questions.