Help!

Thank you for taking the time to read my post and any responces will be nice, thank you.

i have a 1992 gsxr 600
17,000 miles on it
a year ago when i first got it it was great, then when i came up to 3000 miles i did my first oil change.........i put in fully synethic 10w 40
i then noticed i blue smoke coming out my exhuast pipe.......
my first reaction was to do another oil change........this time i put in non synthetic 20w 50 -thicker oil to stop it
it worked great for a while
now i have 2000 miles since i did that second oil change, but i have had to put 1 1/2 quarts in it to keep it full!!! my oil level is goin down, however i cant see any blue smoke......there is however a burning smell on ocassion that has been increasing.....there are no leaks i can see under the engine and i have never once seen oil in my garage!

can you give me any information or suggestions on what to do!!!

thank you

dan