Reduced flow rate (will result in low pressure) is almost always a symptom of damaged resin, usually a result of damage caused by constant chlorine exposure. I suspect your water source is municipal which will be chlorinated.
Was your softener sourced online? Online selling is very competitive, so most online dealers compete heavily based on lowest price. Since the control valve brand and model is most recognized, many dealers will advertise their system is equipped with an identical quality Fleck 5600 SXT control valve, but to achieve a lower price than the competition, cheap imported components such as tanks, lower screen, and resin will be utilized, and online systems will typucally not include gravel underbedding.
Many low quality bottom baskets can be easily crushed and broken, and with no gravel underbedding, there will be no additional barrier to prevent resin from escaping through a broken bottom basket and entering the home's plumbing lines. Reduced water flow through damaged resin, likely resulted in the bottom screen becoming crushed due to greater downward pressure placed on the resin from the water entering from above because the water could not easily flow through the resin.
Unfortunately, low quality resin will usually fail within a short period of time, sometimes in as little as a few months.
One method sometimes utilized to confirm resin damage is to remove the control valve to obtain a small sample of resin from near the top of the tank. Healthy resin when squeezed between two fingers should feel firm and granular whereas chlorine damaged resin will typically feel somewhat mushy.