shortly
If "shortly" means before October, your chances of finding work teaching English in a good school are remote. Work is scarce during the summer vacation, and what few jobs there are have already been taken.
I have completed my TEFL Cert
If it isn't a CELTA, it's not going to be worth much on the job market except outside of the the popular cities I list below..
poznan
The job market is tight in the larger "civilized" cities like Warsaw, Kraków, Wrocław, Poznań and Gdańsk because there is already an abundant supply of native teachers there, both qualified and unqualified. The best jobs with the best conditions and wages go to the best qualified and most experienced teachers. Other teachers have to fight over the table scraps, and end up working in the worse schools for lower wages and under worse working conditions.
Avoid Callan, Avalon and "Direct Method" schools like the plague. They're basically shady operations that pay very poorly, and sometimes not at all. Avoid any school that will not sign a REAL full time contract with you, or that asks you whether they can fudge your tax information.
Never take a job that pays less than 50 PLN per 60 minutes AFTER TAXES. If they can't guarantee you at least 20 hours a week, keep on looking. When calculating monthly income, realize that you are not going to be paid for the Christmas break, the two week winter holiday, and other holidays during the school year. As I said, work during the summer is going to be scarce. Don't count on it, especially in the popular cities.
If you're coming to Poland for fun, experience and adventure, fine. If you're coming here to make money, though, forget about it. You'll be lucky if you break even from October to June, and will most like lose out overall because of the summer doldrums. Very few English teachers make a real good living here in Poland, and those that do are highly qualified and experienced, are good businessmen and marketers, speak the local language well and operate independently.
Forget about giving private lessons. Until you're experienced, the best, high-paying customers won't even look at you. It takes a lot of time and work to build up a reputation and reliable client base, and a lot of business savvy. Hard to do without having considerable savings to tide you over, or with fluency in Polish. The competition is fierce, and never sleeps.
Lastly, about the girlfriend. She will drop you like a hot potato if you do not earn enough to support at least yourself. Think twice about living together with her family. Polish "in-laws" are fine if you're bringing in enough cash to support yourself and contribute your fair share to household expenses (expect to contribute at least 500 PLN for room, and 1000 PLN for board; if they expect more, they will let you know). After the third day of your stay, they will start counting every penny you cost them. Once you become a financial liability, they will very quickly unite against you and start making life hell for you. The best thing that can happen is that they will kick your sorry ass out on the street. Parasites are dealt with very harshly in Poland. Things will ever improve until your "account" with them is in the black, and promises to stay that way for the forseeable future.