I'm having problems with my film nikon slr

Ok so I bought it used
And it's like from the 90's
So everytime I reach like 6 pictures it stops working and says 'err' and the lense stays black
It's happened 3 times
However I haven't been using good film I bought film from the dollar store, could that be the problem?

Sounds like your mirror is sticking in the "up" position. Your camera might need a good cleaning, and lube.

I doubt it's the film.

Although the 1st answer is only a guess, it is a very good one. The camera needs cleaning, and not from you. If you have a local camera store, a real one and not Best Buy, they could at least direct you to somebody, if not do it themselves. With a good cleaning, things should work much better.

Film is pretty much film… The same stuff is sold in the dollar stores as in the drug stores and the camera stores.

Err usually indicates a power issue, and if the viewfinder is black, that implies that the battery may have died in mid-exposure, leaving the mirror up.

The first thing you should do is put fresh batteries in to see if that resolves the problem. The classic solution is to put new batteries in, switch the camera to manual shutter/aperture, and release. That should pop the mirror back down.

If it doesn't resolve, you can try a different brand of film, but it's unlikely to cause a problem unless the reel is particularly stiff.

If fresh batteries don't work, a lube and cleaning might be the next step.

Newer, plastic consumer grade 35mm cameras were not made to last and you're going to start having all kinds of weird issues like this with them as they age. The problem has nothing to do with the type of film loaded unless the film, for some reason only has a few exposures on it instead of 24 or 36. The fewest exposures I've ever seen were 12 though.

It may just be the batteries, but it is unlikely that the camera works okay until the 6th frame repeatedly.

Instead of guessing who is correct here, take it to a camera repair shop or send it to KEH.com to have it checked out. It's very likely that the problem will be expensive to repair and perhaps not worth the cost of the camera. In any case, it's not a problem that random people online will likely be able to diagnose without more details (such as the model!) and not handling the actual camera.

If you want to keep shooting on 35mm, which is totally great, I would suggest buying a Nikkormat FTn or Nikon FM. These cameras do not have automation but they are made much more nicely and make more sense in the film workflow. Cameras such as your current one are sort of cross-overs. They are more like digital cameras in their build quality and features than traditional film cameras and have similar lifespans and numerous issues.

You can buy either of the recommended cameras also at KEH.com for less than it will probably cost to repair this one.