I had this starting towards the end of the first trimester. One visit with the chiro won't do that much. You need to keep going. Remember that your joints are out of whack, and your muscles remember to keep them out of whack, so you need to get adjusted more than once before the muscles learn to stay in the new position. It took about 3 adjustments for me, and I was able to walk across the room at night to go to the bathroom (nighttime was the worst for me).
I'm 23 weeks now, and have been seeing my chiro twice a week, although this week I've gotten bumped down to once a week. Yipee! Sometimes the sacrum pain would switch sides, but mostly it stayed on one side. My chiro gave me two stretches to do and also told me to rub rub rub my round ligaments. When the round ligaments spasm, that can cause your sacrum to rotate. With pregnancy shifting things around, it's harder to keep everything lined up right. But chiro care is helped me SOOOO much. I can actually walk now without thinking the next step might be excruciating pain!
The stretches I was told to do... 1) Sit in a chair and put your left ankle on your right knee. Lean forward ever so slightly while pressing down on your left knee. You will feel a stretch along your thigh, but it also helps with the part above your pelvis in the back on the opposite side (ie, left leg up stretches right side). I don't usually feel the stretch back there, but it definitely helps with the pain, so I know it's working! After you do the left leg, switch to right leg. If your sacrum pain is on the right, you'll want to stretch your left leg a little more, and vice versa. It's the opposite side that's usually doing it (like when my left round ligament spasmed, it caused my sacrum to rotate and my pain would be on the right side)... 2) Step forward into a bit of a lunge, keeping both feet facing forward, and not letting your knee go past your ankle. Keep your upper body straight upright. You should feel a stretch in your lower belly when you do this. I think this was to help stretch the round ligaments, but I don't remember.
Also, when you're changing positions and such, do slow, deliberate movements. That will help prevent your round ligament from spasming. And rub rub rub those ligaments! I will often stand up and rub them right away for a minute to keep them loose.