Is it normal to have watery transparent mucus, and non elastic before period? or is it a sign of pregnancy? have swollen boobs and back ache.

Not pregnancy sign: It sounds like you are familiar with assessing your cervical mucus to monitor fertility. At the time of ovulation, if fertile, a woman's cervical mucus is quite elastic & watery to egg-white consistency. After conception, there is less cervical mucus; typically the vagina is dryer. So I don't think it is a reliable sign of pregnancy. Wait until you miss a period; then take a home pregnancy test:)