Pump Up The Volume

As of late, I have been going to see movies with my significant other and have used up my entire supply of frozen breast-milk. The other night, I wanted to go out and realized I never replaced my supply, so tried to pump right before I went out. Well, that wasn't a smart plan, as I could barely get a drop. My friend suggested I just use some formula, since it was just one feeding. I thought ok, why not? Eventually, when I wean him (I believe I will go until he's about 9-10months) he will start drinking formula before he can drink cow's milk. It shouldn't even be an issue, but the entire time I was out I wondered if I had made the wrong decision to supplement with formula. In the end, he fell asleep sans food and only ate when I picked him up. So I basically worried for nothing.

Next week is the Rihanna concert and a much needed girl's night out, and I vowed (since Monday) that I would pump every night up until next Friday, giving me almost 2 weeks of pump time to stock up my freezer. Well, it's already Thursday and I only started pumping last night. I barely got anything as my body is so used to his scheduled feedings, which are every 3-4 hours. I know if I keep pumping every night my body will get used to the demand and eventually I will able to get a good 4 oz. The only thing holding me back is... well... it's absolutely one of the most irritating things to do. It's not the most comfortable feeling and the pump itself is so loud. It really takes only 20 minutes, and I should technically be doing it right now, but I am finding every excuse not to. :/

So my question is, should I just suck it up and pump or simply incorporate some formula to my son's diet for the times I want to go out? Will my supply go down, or stay the same? Any advice is welcome!