Piriformis syndrome is a not so fun condition in which you Piriformis muscle, which is located in your butt, starts to spasms and cause pain. It can also compress and irritate your Sciatic nerve that runs from the bottom of your spine and down your leg, causing pain, numbness and tingling sensation in your butt and or in some or all parts of your leg. This symptom is called Sciatica (or: Sciatic Nerve Pain), and you can read more about it in this post: Sciatica In Pregnancy.
Gentle Strength exercises, classic ones, can be a great way to get your Glut. muscles in your butt to fire up more effectively, and lower the pressure off of you Piriformis, and then get it to calm down. In the next video you'll find exactly that: Exercises that can help, very basic and suitable for pregnancy.
Try to perform them twice a day, ten repetitions per exercise: 1. Glut. activation on all fours 2. Clams 3. Leg lifts 4. Leg circles: front & back 5. Bridge with but squeeze In addition, it is also important to stretch and lengthen your back and you legs, take a look at this post to learn more.