first thing first, are you checking the oil level correctly? was the car parked on a leveled surface? to check oil level, start the car that has been parked overnight for about a minute. turn it off and then check the level. this is the correct way to check level whereas we normally just check the cold car that has been sitting in the garage overnight by taking its dipstick out. 2ndly how much has the oil reduced? if the oil is still between top and bottom level of dipstick then it is no big deal. do not switch to thicker oil just to cover the real problem. use recommended oil grade and viscosity as stated in the owner's manual. plus you can do the following to check it further.
check PCV valve by taking it out and shaking it. it should be making a rattle sound upon shaking. you can also check if it is working properly by blowing air with your mouth from both ends of PCV. it should only allow air from entering from one direction i.e. one end should be blocked.
if PCV is ok, and there is no visible oil residue on exhaust, spark plugs, then it could be just a minor leak somewhere. if there is also no leak, then it could be a counterfeit 2 number oil that you purchased. so my suggestion is dont worry, drive the car around, check oil level after 500 or so kms and then check how much level has gone down from today's point. the problem might just vanish upon next oil change. always buy oil from authorized dealer so that one is sure oil is genuine. which brand of oil are you using BTW?
