Tylenol (acetaminophen) isn't working the way it used to. Can I increase the dose without hurting my liver?

Maybe. In the absence of contraindications Acetaminophen may be taken up to 1000 mg four times per day for short periods of time.
Depends on dose. Tylenol (acetaminophen) in high doses taken for long-term use can damage the liver. Your liver isn't any more sensitive to tylenol (acetaminophen) during pregnancy than any other time. You should not exceed the limits outlined on the bottle. If you're having enough pain that you have to take tylenol (acetaminophen) through the day, every day, you should talk to your doctor and see if you can eliminate the cause, not just treat the pain.