Do have an separate AC units for upstairs and downstairs? Where are the return vents for the upstairs unit? Does the return vent have a filter? If so, when was the last time you changed it?

Yes, we have separate units for upstairs and downstairs.. the return vent for the upstairs unit is upstairs in the ceiling. yes it has a filter and I changed it last week..

If you are having negative air pressure problems with all upstairs room doors open, then the return is either undersized or the duct work is disconnected. Can you follow the return vent in the attic?

How long has this been going on? Did you recently make changes to the AC?

no changes to the ac unit at all.. I can call someone to check the duct work and apparently it has been going on for a while... we just noticed it.... Is there anything else you recommend they check when they come out to look at the exchange? I would like to get this figured out in one visit.

Do you have a powered attic exhaust fan? This could be a problem if you don't have adequate attic ventalation. I would ask to check the blower speed on the AC. It may be set higher than it needs to be.

Do you see any differences if you remove the filter from the return? Your filter may be too restrictive or too small.

"pulling outside air from the chimney and under doors"

pulling air around damper in chimney?
under interior doors that are closed?

please clarify.

how did you discover this?

best of luck.

have them do a static presure test on the duct system. then adjust fan speed /repair duct work as needed.
This could be a dangerous siuation/unhealthy

called my Air conditioner company and they kinda acted like I was an idiot... Told them what everyone asked me to check and he half assed checked everything and told me that the house just needed to breathe and for me to take off the plastic I had taped over the fire place ( the humidity was coming in from there and I covered it so my carpets would not get wet) and then said it would normalize on it's own in a few days... I was not happy that he was kinda acting like I made it all up... so my partner went up in the attic and went searching for a leak in the duct work. It was right beside the unit where the main duct attached. but you had to put your hand under there to feel it. Which the repair man did not do.. so we called them back and showed them and got that patched up and poof it's all better now. Thank you everyone for your suggestions

Thumbs up for mike_home. Thumbs down for the OP's HVAC company.

so now you don't have the draft at the fireplace
and under whatever doors interior/exterior
open/closed as before you had duct sealed?

hard to believe that one leakage site
caused all of that.