As it has already been said, Tylenol is safe. You can also use a heat pad for short periods of time, as in 30 min on, 30 min off.. Yoga and exercise to stretch and release tension. Warm baths, massages..
If this is a recurrent problem I would definitely start an exercise plan and schedule a visit to a chiropractor to help me with massages and whole body posture. Due to weight gain and hormonal change your body posture is slowly changing and adapting, and frequently derives in bad postures.
Hope it helps!
Look up yoga for pregnancy on YouTube I've used it with both of my pregnancies and it has done wonders with my back issues
Regulare strength is okay but only for a day or two then you should let your dr know.
Try a heating pad and as odd as it sounds go for a short walk and do some back stretches. My lower back aches all the time and doing those things helps. Also my husband lightly massages relaxing oils on my lower back. We use bath and body works stuff the relaxing mint
Tylenol is perfectly safe to take during pregnancy