Having a similar chronic pain in my low back, I know how you feel. I work in athletic training and work with many physicians and here's what they would tell you.
First, your OB/GYN controls what medication you take and when. Occasional use of tylenol vs. regular use of tylenol may make a difference. Unfortunately, you don't have any other pain med choice. While I'm sure your chiropractor is looking out for you, one only physician should guide your care at this time.
Second, I found relief with prenatal water aerobics through my hospital, Good Sam. I could stretch my hamstrings and quads and exercise but without the loading.
Third, I had a prenatal massage that focused on my low back/SI/spine and found relief that has lasted 5 weeks (I'm being induced tomorrow).
While these things may not work for you, I think it's important to follow the advice of your OB/GYN for treatment. If the pain doesn't resolve after delivery, see your PCP/orthopedic/chiropractor for care. Like I mentioned earlier, I work with many physicians in the western suburbs and could give you a referral if needed.
Best of luck! S.