I did not want to answer on this long thread because it would get lost, but since this comes up like every 2 days here are my 2cent.
1) Digestion tract slows down its work to better absorb nutrions while pregnant which causes all kinds of upset stomach and bloat.
2) Rib cages dont spread that early, but you might retain water (your blood volume shoots up in the first weeks of pregnancy and continues to raise throughout) and gain fat reserves (see slowed down digestion) - this is needed to sustain the baby.
3) Love your bump, whatever it is. As long as its in a healthy range, dont worry about weightgain. You have a baby to grow.
Stepping of my soapbox...
Re: Bloat & Rib cages spreading - Re: Showing at 5 weeks