I have spider veins at 19. is it becuz im preggers?

In part, perhaps: 1st, congrats! spider veins occur due to many factors, genetics/hormones are significant culprits. In pregnancy, estrogen/progesterone levels are higher than baseline; there's a higher circulating volume of blood & growing baby can put increasing pressure on veins that drain your legs. Such factors lead to venous insufficiency->varicose/spider veins. Consult a phlebologist re post-partum treatment.

Pregnancy + genetics: Many people first notice spider veins during pregnancy. Usually there is also a family history of veins. Normally spider veins improve to some degree over the first few months after delivery. Veins generally get worse with subsequent pregnancies. Graduated compression stockings may help minimize worsening of the spider veins as well as symptoms (such as leg heaviness, aching, etc).

Probably: Risk factors for spider veins, and underlying venous disease includes pregnancy, heredity, obesity, female gender, lifestyle (working/standing long periods), aging.

Heredity and hormone: Heredity is the main factor that determines who gets veins, then increased chances with female hormones, each pregnancy, prolonged sitting, prolonged standing, hot climates, heavy lifting job or heavy weight lifting recreationally. Some veins may go away after your pregnancy others will need to be treated.

Many factors: The most common cause of spider and varicose veins are hereditary factors followed by pregnancies. The more pregnancies the greater the chance of vein formation due to stretcthing of the vein valves causing reflux(leaking). In general when veins occur at an early age there is a strong genetic component. After pregnancy there should be some improvement in the veins. You should see a vein doctor.

Probably: That surely doesn't help. You must have had a parent that had bad veins as well! Poor girl, only 19 with spiders? They'll improve after you deliver though.