Using a sub woofer that is not set up properly will tend to make your mixes exactly like they are.... light on the bass end since you hear massive bass in your room, you turn it down until it sounds right to you and as a result, the mix is not balanced.
Check the mix on some fairly decent headphones that give good response.
You don't need high dollar speakers to mix right, you just need to learn the ones you have and know what they are capable of....strengths and weaknesses. I have some small 5" speakers and a sub, however, I took great pains to get the levels of both balanced so what I hear is what the reality is on the DAW mix.
Don't shut off the sub, but do turn it down several DB and try another mix. Both my speakers and sub are down. Speakers at 50% and sub is set to be properly balanced at that level. Once set, I don't touch the levels again.