Sewer gasses need help!

I’ve been slowing feeling weak and bad headaches when I go inside my 4 month old manufactured home recently. It’s gotten pretty bad and I’m
Not sure why it’s happening. It’s coming from a kitchen sink and recently started in the master bedroom sink. (They share a roof vent). They all have brand new air admittance valves and I changed them anyways to try. Made sure there’s water in all p traps. Still no luck. The only symptoms I can see is that the master toilet does not flush very strong compared to the other toilet on the other manufactured home. Also the shower doesn’t drain very well. Could a small clog cause all this odor? It doesn’t smell like rotten eggs I’m assuming because it’s a new build. One plumber told me he smells nothing but to me it comes and goes. It gets very strong when dishwasher is on or shower is running . Sometimes at random.