Need help

I’ve looked online and it says this can be caused by one of three things, intake manifold, head gasket, and lastly, just some condensation from cold climates; it’s now getting colder where I’m from and this began happening. Every drive creates a little more in the gas cap. Any ways that I can try to diagnose what the issue is before spending a bunch? Also my oil from my dipstick is clean, no water/coolant in it. Anyone else have this issue? I park my car outside in the grass too if that matters. Also I’m not driving it unless I check the oil to be clean first.