High CK levels are common in bodybuilders and athletes for two reasons: 1) we use creatine and 2) we train hard. Both are known to increase CK. The best thing to do is to take a week off training and creatine before your next liver enzyme test and you may find that your CK returns to normal. If not take a month of creatine (to bring levels back to baseline) and a week off training before the next test. If CK is still high, then you may have a legitimate liver problem, which you need to discuss with your doctor (as I'm not qualified to diagnose disease).
Many Skinny people think they have a high metabolsim blah blah. the truth is, if you nibble on biscuits n stuff that really dont have much protein or starch, you wont gain anything. if you want to gain weight you have to sit down n eat like u nuts. meals you cannot afford to skip are breakfast n supper. always eat alot before you go to bed. u will always wake up hungry n wont have to really force breakfast in. its not that you dont eat. its jus that you dont realise that u fill up your stomach with air n water. another thing, try working out. the problem with skinny people working out is that they dont realise that spending the whole day in the gym actually works against u. YOU GO TO THE GYM TO BUILD MUSCLE NOT BURNM FAT! spend a maximum of 45 minutes in the gym n learn to rest your muscles. use heavy weights and do 3 sets of each rep. dont rest your muscles till the 45 minutes are up. drink lots of water too.