Thick sperm is not a medical terminology. Probably, you are talking of thick ejaculate or semen not sperms. Having thick semen is not a weakness, it is an advantage because thick semen means good quantity of sperms in single ejaculate. Before jumping to conclusion about your sperm quality, get semen analysis. Normal sperm count should be 40 millions per ml with 2-3 ml of ejaculate. Out of these sperms, 70-80% should be motile and out of these, 25-30% should be fats moving. Sperms should not be non motile, dead or deformed. So, get semen test.