Too big too fast

So I'm like 7 weeks pregnant and already tired as ever. My back be hurting sometimes and this is my 2nd child but with my first one I didn't experience this till bout 6 or 7 months. What could this mean? I need to lose weight? I haven't been sick so fair which is good but I'm just tripping  out how tired I am and it's so early. Any advice or suggestions? Thanks in advance