Welcome at health care magic.
It looks from your details that most probably you may be having one of the following-
-Sacro iliac strain
-Prolpased intervertebral disc
at your lower back
-Simple back strain
The abnormal posture is one of the reason which does contributes to all this.
There are some other reasons like injury
to your back,spondylosis
,etc. which can lead to these problem.Before going forward you should do following-
-Have a x ray of your back.The MRI will be best to check for a problem at back.
-Get basic blood investigations like TDLC,ESR to check for presence of an infection.
You should do following to have relief in this-
-Take a good analgesic
like advil or aleeve.
-Do strict bed rest
-Do warm fomentation at your back with help of a red rubber bottle available OTC.
Hope this will help in relieving your problem in next 5-7 days.
Wish you a happy & healthy life.