Do you have to play the clarinet before doing bass clarinet?

You don't have to, but most band directors, and myself, would recommend playing regular "B flat" clarinet first. It helps you to get used to playing a woodwind instrument and playing on a reed. It also helps you to build up enough strength in your lungs to be able to blow through a bass. Blowing and sustaining enough air through a bass is very difficult without building up to it first. It was hard for me to even play a regular clarinet when I first started playing. HOWEVER, If you really want to just play bass, and have time to practice, you should be able to achieve your goal. It would be very hard though.

Put your mind to it, whatever you decide to do, and you'll get there! Keep trying! Good luck and I hope I was able to help:)

I would recommend playing the regular clarinet for at least a few months before switching. As the poster before me noted, it takes time to build up the lung strength to play an instrument, especially if you haven't played a wind or brass instrument before. I would also point out that a bass clarinet has a much bigger reed than a regular clarinet does. I had to start with a very soft reed on the regular clarinet to build up the muscles around my mouth before I could move to a thicker reed that produces a better sound. A bass clarinet will take even more mouth strength because you have to use more wind and a stronger mouth grip (called embouchure) to produce a good sound.

That being said, once you know the regular clarinet well it shouldn't take more than a couple of weeks to be a decent bass player.