Laying on the left side was fine, then I decided to get up (not abrupt…

Laying on the left side was fine, then I decided to get up (not abruptly), even didn't manage to rise, as I got a clamp under my right breast in the ribs area. Can't lie on either right or left side, and during rising there are also spasmodic pain sensations. Don't feel anything when lying on back, but they say it's not allowed to lie on back during pregnancy. What could this be? How to relieve spasm?