i had never done laundry at this house before until after I remodeled it so it could have been messed up before and i wouldn't have known but as far as i know nothing is vented and the washing machine doesn't have a trap does the washing machine need a trap and does everything need to be vented or can i just vent the main pipe somewhere in the middle ?
so were do i need to install one at and will it make the underside of my house smell or do I have to tie it into the main vent that is attached to the side of my house?
The washer needs to be trapped and 2" trap and 2" standpipe.
Shower needs to be 2" and also trapped
Vanity can be 1 1/2" and sink need to be trapped.
I find it hard to believe that the fixtures are not vented and the vent may be concealed in the walls. But anything is possible as far as not being vents. It's hard to diag via the internet and at this point I would steer you to contact a local plumber and see if he/she could come by and evaluate your plumbing system.
On this forum every DIY'r here will tell you to just stick an AAV (Air Admittance Valve) every where. Us plumbers will do almost anything not to install on. Why? Because after month to years of gnats, spider webs, dirt/dust and wht ever else gets into the seal of the AAV it can plug open or closed and cause problems.
It may cost a few dollars but at this point I think it would be money well spent for an evaluation of your system.