I get pain on right side back.

You haven't given me enough information to help you. How far along in your pregnancy are you? Does the pain come and go or is it constant? How long has this been going on?

I am a man . And I am just getting lower back pain . I did a ultrasound and it was good]

I will move this from the Pregnancy forum then.

Wouldn't be the first time a "man" was pregnant.

Possibly a nerve issue. What is the follow up from the ultrasound?

You are not being helpful at all. Please be very specific about location and type of pain, and if it radiates out, and any thing you might have done to strain yourself rather than disease. How you sit all day, how you sleep, what you lifted, running along a road instead of a track, on and on...

Injury to muscle or tendon
Pinched nerve

Kidney problem
Pneumonia on one side, believe it or not, can be lower back (and not have coughing)
Appendicitis, just because your appendix is on the right, although in the front
Any number of more rare conditions