According to Planned Parenthood, when practiced correctly, the withdrawal (or pull out) method is effective in preventing pregnancy 96% of the time. That means 4 out of every 100 women who use this method correctly will still end up pregnant. So yes, there's a chance you could be pregnant, but the odds of not being pregnant are certainly still in your favor.
Since you're not sure when you ovulated, and since you have irregular cycles, I would start testing for pregnancy no earlier than April 3rd and then if that test is negative test every OTHER day until the arrival of your period or until you get a positive test.
Since you don't know when you ovulated it's entirely possible that those symptoms right after "ovulation" were actually ovulation symptoms, which many women (including me) experience.
The chances are good that you're not pregnant but if you are, then there are lots of resources available to help you find the best path for you going forward.
And if (most likely) you're not pregnant check out Bedsider(dot)org which is a really awesome website that breaks down each method of birth control so you can make sure that you're using the one that gives you the most confidence!