More plumbing issues
Based upon your description and comments, I am going to guess that the trouble lies with your septic system not draining (or barely draining).

If you are new to septic systems, there is a lot of useful information online about the theory of operation and the different models commonly in use.

Regarding the "pump the tank again in 2 years" advice, that is boilerplate advice from a septic pumping company and it says nothing about the condition of your system, other than the tech servicing it thought it was working.  With a properly functioning conventional system and 2 people living in a 3-4 bedroom home, provided no one flushes a garbage disposal or anything nasty down the drain, the pumping interval can often be extended to 5 years.

On the other hand, if your drain field is mostly plugged then you will begin having trouble about 1 month after it is pumped, since that is roughly the time it takes for the empty tank to fill.  A failed drain field will not necessarily cause water to pond near the surface.  For example, one such failure occurs when more than just clear effluent leaves the tank into the drain field.  After awhile, that condition looks like this:



If the drain field pipes look like this then there will not be visible wetness and the sewage is going to go the only other place it can --back into the house.