When you orgasm, you're NOT supposed to ejaculate clear, liquidy fluid. It is supposed to be thick, off-whiteish and, some may say, sticky. Some people often mistake the off whitish hue of semen for yellow, which is common. I don't think there's anything wrong with you... especially an STD. If you're in pain or discomfort or are ejaculating pink or red coloured semen, then you should immediately see the doctor.