Forum:More weapons slots?

I'm playing as mordecai,still in the first playthrough in arid badlands.I recently levelled up to 13.However i hav found that i am still left with only 2 active weapon slots.from what i've seen in the inventory,there are a total of 4,but my last 2 slots are still locked.How do i unlock them?Do i have to lvl up?How much more?Also i want to expand my inventory as it can currently hold only 12 items.Can i expand it by some way?