I didn't have a chance to read all of the responses before I wrote, so I hope I'm not repeating too much! :)
First of all, I want to compliment you on your wanting to give your little guy breast milk. Good for you! I exclusively pumped with my first little gal after she was 1.5 months until she was 12 months. I just wanted to share the ins and outs that I experienced with this.
First, it takes lots of time. So, if you decide to do it, just be prepared for that. You HAVE to do it every 2-3 hours (except a break at night) or your milk will dwindle away. You can space the time out to 3-4hours once your baby has started eating a lot of solids, and your milk is strong. My daughter usually ate between 20-30 oz a day, depending on her age, so you have to make sure to make that much
Also, everyone's let down/milk supply patterns are different. So, pumping could be more time consuming for some, and not so bad for others.
Pumping with even 1 kid for me was tricky (I have 2 now), you need to be prepared for how you are going to handle it when baby cries / needs you when you're pumping.
Because you have to pump for 20 minutes each feeding AND feed your baby each feeding, it can be extremely time consuming. It DOES make it easier when you can master the task of pumping and bottle feeding at the same time. It's not as cuddly though. I had a wiggly baby, so I would just sit her in her carseat and hold the bottle with one hand, and pumps with the other. (I also swore to never do it again, but that's just my two cents)
You have to stay on top of growth spurts, and sometimes pump more often for a few days to increase your supply. This was kind of a pain, but do-able. Drink plenty of water! Remember, your baby will only eat 2-4 oz now, but later it could get closer to 6-9.
Find a pump that is easy to haul around, and preferably one with a wall plug, and a car adapter for long trips. I used to use it in the car if I HAD to, just covered up with a blanket while my husband was driving.
Anyway, I hope that info helps. That's about all I can think of right now! As for advice, if you have it in you, I'd give it another few weeks. Sometimes that first 1-2 months can be rough, but it usually gets better. And, if it doesn't, I can definitely tell you that I (and many, many other people) have had success pumping exclusively. It does work!
And lastly, don't be hard on yourself if it doesn't work out. Remember, you have a little three year old running around too, it could be tricky to pump and keep up with 2 little kids!
Good luck to you!