Since the tub is new, it was likely wet-tested and the water not completely removed from the piping so biofilms may have formed. If you did not do a decontamination procedure when you initially got the tub, then that might be part of the problem. It is important to decontaminate a hot tub when you first get it. This is through a combination of using Spa System Flush (which helps remove biofilms and grease) and then high levels of chlorine (100 ppm).
However, if you are using the tub daily and are not adding chlorine after each soak, then the problem could also be simply that you are not dosing with enough chlorine properly. If you do not have an ozonator (we need to know if you do), then every person-hour of soaking in a hot (104ºF) tub requires around 3-1/2 teaspoons of Dichlor or 5 teaspoons of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. If you aren't measuring a residual of at least 1-2 ppm FC at the start of your next soak, then it is the zero FC from using too little chlorine that is the cause of the problem.
Note that once you have decontaminated the tub, then if you properly maintain chlorine levels and dose properly after each soak, then you should not need to shock.