I have been a vegetarian for 15 years now.
Your body is adjusting. Its normal that your shit smells really bad for some time. I do not remember gass though. This might be a result from all the fruit you are eating. I also dont remember feeling weak. Are you eating enough? Meat has more calories as fruit does...So you should eat extra.
There is more then tofu as alternative. Just go to the supermarket and check out the vegetarian section.
Millions have gone before you and survived...
(btw..Serena Williams and her sister are vegetarians..they have lots of energy)