3. Ya best to avoid bigger sized fish like tuna (reason being, the bigger fish is at the highest of the food chain n hence, their diet might consist of many other fish/prawns which eat stuff that consist high mercury too.) some doc advise against mayo too cos it consist of raw eggs. So depends on how strict you want your diet to be.
4. Showing of tummy? My tummy only shows a little bump during 4th month.