I am sorry your kitty is having trouble. I think she may have a urinary tract infection, and would like for you to take her to the vet first thing in the morning. The symptoms of a UTI include frequent trips to the box, or urinating outside the box, very small amounts of urine passing, blood in the urine, a strong smell to the urine, and sometimes urinary blockage (very rare in females but life threatening none the less). This is an extremely uncomfortable condition and can progress into a dangerous kidney infection if left untreated. Having your kitty seen tomorrow, before your vet closes for the weekend will save you alot of money in emergency vet bills, and will make you kitty alot more comfortable. She will need an exam, urinalysis and some antibiotics. Pain medicines or anti-spasmodics may be needed as well as the spasms associated with straining to urinate can be quite painful. Please see the following website for more information on uti.
Please try to have your kitty seen tomorrow so that she can start to feel better as soon as possible. Please let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Good luck with your kitty!