For chronic lower back pain that is fue to soft tissue damage, is it better to take aspirin, ibuprofen or acetaminophen roughly 3 times a week?

I have never heard: I've never heard that taking pain medicine three times a week is any better for treating low back soft tissue injury. In order to take full advantage of the anti-inflammatory effect of Ibuprofen or aspirin, it needs to be in your body all the time, and can take 7 to 10 days for full anti-inflammatory effect. Until then, is only a pain medication. Tylenol (acetaminophen) is only a pain and fever reducing medicat.

Any if them: Taking any of those medications is fine- just take as prescribed. Stretching and exercises are equally important if not more.