Oil leak or the engine is burning oil.
It would depend more on how many miles you go before it needs a quart of oil. A healthy engine should go between oil changes without adding oil.
oil leak, worn rings burning oil if only a quart or two between oil changes not too much to worrie about on some engines but would have checked out.
When I was doing my own oil changes I would prefill the oil filter and then put that much less into the engine , but any place that changes oil does not have the time to do that
I would recommend at least every 75,000 miles.
Someone would be able to find coupons for discounted oil changes at bradsdeals.com, and also they would find coupons for discounted oil changes at couponcodes.com
Leaking? Burning due to wear of internal engine parts valves or rings
Yes...Some synthetic motor oils recommend 15,000 miles between oil changes. However they also recommend changing the oil filter at 7500 miles then adding more synthetic oil to replace the oil lost from changing the filter. In summary...drive 7500 miles change filter,add oil, then drive another 7500 miles. Read the recommendation on the oil bottle.
Change oil every three months
You don't. Add not additives to your oil. If additives worked the manufactures would add them to the oil and recommend you also do so.
your oil should be topped off whenever it is below the add line which is 1 quart low and changed every 3 months or 3,000 miles How fast does it go through the oil? You'll be ok if you add when it gets to the add line, and fill it to the full line. If you're going through more than a quart between oil changes, you're using too much.
Find the oil reading when the car is cool. If the oil is full, add additional oil to the crank case. You can also add a pint of upper cylinder cleaner to the oil. Test drive to see is there are any changes.
It shouldn't use any between oil changes.