Are cardio exercise needed every day?

No, you probably should not do cardio everyday.

Reason 1: Working out damn near everyday leaves many people in a state of never really feeling rested. Their minds and bodies have a perpetual ache and this limits their effort and motivation.

On the off days, going for a long jog will only slow your recovery. Many joggers have a tightness in their legs that lingers during the week. This will also beat up your joints with the constant pounding of your feet against the ground.

All exercise forces some system to recover. The central nervous system, which acts as the command center that directs muscle throughout your body, can get exhausted from too much exercise. So even if your muscles seem ready to go, other systems may break down if you train too often. Those whom get too little sleep often fail to improve, as their central nervous system operates poorly even if their muscles feel fine. Too much exercise affects you similarly.

Reason 2: Doing cardio on rest days is generally unnecessary to build muscle and/or lose fat.

If your primary goal is to build muscle, then there is no need for doing any cardio on your off days. Similarly, if you want to lose fat but you're creating your required caloric deficit through diet alone, then again there is no need for doing any cardio on your off days.

In both of these scenarios, the only thing you truly need to do on your rest days is... rest. Cardio isn't needed at all and you can avoid it completely. That doesn't mean you MUST avoid it, it just means that these are two common examples of people who CAN avoid it and still reach their goals just fine.

I have said time and time again that you can't outrun a bad diet. In the same vein, when you have your diet in check, there is no need to do cardio when you are better off resting.

If either of these examples describe you and you have no other reason or preference for doing cardio, then your answer is pretty clear. Don't do any.

Why is it that I can't seem to gain more than 145 pounds even though I workout 4-5 days a week, take in plenty of protein in addition to regular meals?

What's plenty? What's regular meals?Obviously plenty of protein and regular meals are not doing it for you. I'm guessing since you didn't say I eat 250g protein a day with 3500cals total per day- that you are not tracking how much you are eating.Start tracking what