Back pain can be due to several reasons however lower back pain is an indication of certain injury. So, I am curious to know whether you've pulled a muscle or have a muscle strain. Whatever the reason maybe you should avoid lifting weights. Other reasons can be arthritis, osteoporosis, or a slipped disk, etc. While my rough guess would be a muscle strain, therefore, consult your physician and take some OTCs drugs for symptomatic treatment. You can refer this for choosing the right OTC for you.