Should I help my baby sit up?

Almost 5 months, baby rolls over, does "push-ups", good head control, but without keeping it completely steady.

Even with tummy time or trying to encourage him to sit by pretending to lift him by his hands, he still isn't interested in lifting his upper body. I am seeing his pediatrician and orthopedic doctor in 10 days, but until then I wanted to know how did you handle this?

Should i wait until he starts lifting his body by himself, should I encourage it by propping him against pillows, what did you do? His trunk muscles might not be very strong as he hunches a lot.