As per your explanation I understand you have got
back pain first time. And it is continue on your left side back. You have done urine test and it is normal.
Here I suggest there are different resion of back pain along with
abdominal pain like kidney stone,
ovarian cyst, urinary track infection, or can be
muscular pain of spinal lower back muscles, and can be related to lumbar disc problem too.
Here since you have experience it first time as well there is no symptoms like numbness and
tingling in legs means it can not be related to nerve and disc.
As well urine test is normal means it can not be related to
urinary tract infection.
Next is kidney stone problem, and ovarian cyst how ever the conformation can be done only with
ultrasound abdomen. I suggest to go for it and take treatment according to report if any thing gets diagnose.
Suppose if ultrasound report is also normal then it can be gastric problem and for this take anta acid tablet, avoid spicy food, have good amount of water, and change your food habit keeping it regular, simple and have balance diet with regular fruits and fiber rich diet.
For back pain I suggest it will be muscular back pain for this consult a physiotherapist and here the physio will guide you for further treatment , postural change, as well spinal exercises. You can just follow all along with hot and cold pack use on your back. In combination all above treatment will help to reduce inflamation, relaxes soft tissues, and so that will help you for pain relief.
Take care.