What Causes Foul Smell On Burping Or Passing Gas During Pregnancy?

im 17 weeks pregnant and everytime I burp and fart it smells like rotten eggs it started today and the smell is getting worse what can I do
also for the last week I go to the bathroom and to do number 2 my stool is very soft it looks like when you take diet pills and you can see parts of your food and fat on it should I be concerned