Tourist visa

It would be at the discretion of immigration when you return. I would not even mention the fact that you are working or have worked in D.R. that would only complicate things. I guess if they ask, you can always say you are living on savings. I'm not surprised at all that you have managed to work and live in the D.R, under the radar.  I have met countless folks who do it and do quite well, but I often hear many saying it can't be done.  It is not the legal thing to do, but not impossible! There is always foreign business owners who would much rather hire foreigners as opposed to locals who may not necessarily have the same work ethics as their foreign counterparts.  If you must roll the dice and have to leave and then return, you might also want to consider which airport you return back to, since in my experience, some are a bit more lenient than others. Punta Cana, and Santo Domingo seem a bit more watchful, whereas La Romana, Samaná, Santiago, and possibly Puerto Plata seem a bit more flexible. Safe travels

Yes you will pay an overstay fine when you leave.  It is unlikely you will have an issue reentering but it could happen.

The days of easily finding a job without residencia or a work visa are gone. The govt is fining the employers who are caught. That is why it is harder. Foreign owners of local companies are scrutinized and held to tougher standards.

Many expats arrive with jobs in hand, many of them online.  It is not actually fully legal but isnt quite the same as working for an employer here either.

You should consider getting yourself legal honey!

On the leaving card, don't fill in the 'how many days'' you were there place; if they question you, tell them it was a bit longer, but you were sick and shacked up with your local wife, now are well enough to go to the states to get patched up.  Tell them you understand you mighthave to pay a fine, and have a few thousand in your hand that they can see, and I'll bet the 'fix' it all for you.

But will I get an overstay stamp in my UK passport ?  What happens when I get to the US will they allow me in to visit for a week as am going there with my girlfriend, then will I be able to come back to the DR thats what I am trying to find out.

No overstay stamp.  It's an exit stamp.  They would have to look at both your last entry and exit date and know the law in order to see that you over-stayed.  Not likely even returning to the DR that they will be able to calculate that it was an overstay yet alone anywhere else you travel to...  No worries, pay the fine if they ask you to and that's it.