Replaced muffler and now exhaust in cab?

I have a 98 single cab 2.4l manual .I just replaced the muffler from the o2 sensor back. Now there's somes fumes getting in the cab no smell more of a feeling nose irritation and when get out of the truck light headed. There are no visible leaks or no noise .
Is it possible to have back draft from tail pipe it looks to be in the same position?

 

Have you checked the welds???exhaust shops are bad about not welding the top of the pipe due to odd angle seen it many times just a idea to look at or possibly a pin hole....

 

If you can't smell it, and get light-headed, it could be CO poisoning.
Don't go on any long trips without having that checked out. If you have a battery-powered CO detector in your house, temporarily put it in your truck and see if it reacts.

 

also make sure the doughnut gaskets aren't bad at the manifold or the cat flange gasket. lots of times they don't replace these and they WILL leak from all the pipe movement of replacing the muffler so they need replacing anytime you take the pipes apart from the cat or the pipe is moved around.

 

Take it back to the place that put the muffler on and tell them what you are experiencing. They may have missed something.

 

Thanks im taking it back today,

 

Thanks everyone for your input I will take all the advice and go back to the shop and get me a co detector just to be sure thanks again!