septic issues

I have septic problems. It started with soap bubbles in toilet during washing machine spin cycle, and slow flushing toilets. We now have , especially on rainy days, stinky septic water and gunk coming up in toilets and bathtubs, even out from under one tub. We also have a spot in the yard that stays wet and stinky. We've had tank pumped and drains snaked. We are a family of 5, two adults and three teenagers, three bathrooms and a laundry room that seems to be in constant use. We have been told that we should add some additional field lines. We have 300 ft and have been advised to add another 300 and a flow diversion valve, which if I understand correctly means that we still will only be using 300 ft. at a time, so I don't see how that will improve things. Seems to me it would be better to just have 600 ft all being used at the same time. Am I just a dumb lady or can someone explain it to me before I spend alot of money. Any opinion appreciated. Thanks!

Sounds like a saturated leaching field causing your problems, water isn't moving the way it should once it leaves the tank. I would get estimates from 3 reputable septic tank installers, check with the BBB. They all should be talking the same lingo about your situation. A perc test normally tells the story if you topsoil is any good or not.

Thanks for input. Just today I have noticed a really strong almost gassy smell in one of my bathrooms seems to be really strong under the sinks and vanity, could that be related to the other problem?

If the system is clogged and water travels towards the obstruction, then air displacement takes place whereby the drains will belch back sewer gas. There are many possibilities to the smells you have, could be just leaking drain lines underneath your sinks.