I've been training for 2-3 weeks, I've been working out with a trainer…

I've been training for 2-3 weeks, I've been working out with a trainer at the gym for a year now, but I do moderate workouts at the moment, listening to my body. Should I go see a doctor and get checked up? The symptoms are that my lower back hurts sometimes and my stomach feels sore, I read this is normal for this week as my body is restructuring itself.