The tests are pretty accurate, so you could take another one but it's unlikely to change the results.
You might want to pick up some ovulation tests and figure out when you are ovulating for better results. I went through fertility treatments and discovered that I ovulate on about day 10, not day 14, which meant a way different time period in which to try and get pregnant.
Having your period does not mean you are ovulating regularly, and if you aren't ovulating you aren't going to get pregnant. I also got pregnant very easily the first time. But after that - well, it was 7 years before I got pregnant again (miscarried) and then another 8 years before I got pregnant (baby boy last year), and all of that was spent without birth control and very regular periods. I never missed one. The regularity/irregularity of your periods isn't a good indicator of fertility.
You might want to consult with an RE or at least your OB/GYN if you're having irregular periods. That's not normal, and indicates hormonal imbalances that could interfere with getting pregnant. There are simple drugs the OB/GYN can prescribe to help with that if there's no underlying issue. But really, do it sooner rather than later. The sooner you figure out what's going on with your body the easier it will be to get pregnant.
Because you don't have regular periods, it's going to be hard to tell if you're pregnant or not. Best bet is to use an ovulation kit. Many RE and OB/GYNs won't start fertility testing until you've tried (and failed) for one year. That's the definition of medical infertility and that's when they'll start doing tests/treatments. If your OB/GYN or an RE won't talk to you about it before one year, you'll want to chart and track your periods/ovulation until then to see if you can figure out when it's best to get pregnant. Remember, there's only about a 24-48 hour window, so nailing down the right day is important.
Good luck!
L.