2016 Peterbilt Mixer Truck

99% of trucks on the road don't have an oil level sensor and maybe about half have a coolant level sensor.

 

Most big engine dipsticks generally have a range of a gallon between add/low mark and full mark. So if not on stick…..

 

Probably.
Open the cap, smell it, look inside.
You should be able to tell.

 

If you'only' drove it for a few days; you should have checked it on day one.

Every day is best, you will see some consumption over time and catch any sudden and possibly engine damaging leaks.

Sometimes a series of fleet trucks will have similar consumption.

Old R model Macks were famous for blowing the top few quarts out the breather [way before emissions on diesels] every day.

The fuel person soon learned to leave the oil level half way between the marks to avoid the drivers who were fed up with smelling it.

Every truck in the barn would not need much oil if left a touch low and the drivers were not smelling it every day and everyone was happy.

 

If oil pressure went up because you added oil you were out of oil! Not good.
Check oil, if low add oil. Give it a minute to get in the pan and then check oil again. Repeat as necessary. Most large trucks hold 10 gallons. So if it's way low on the stick it may take a few gallons. But I dont know what engine you have.