First, if you're still bleeding, then I think you should hold off on taking a test. It's true, implantation bleeding and menstrual bleeding can sometimes be similar, mainly because they usually take place around the same time. A good way to tell the difference between implantation bleeding and menstrual bleeding is by the length of time you're bleeding for. If you experience bleeding and spotting for just a day or two instead of having an average period for 4 to 7 days, then there's a good chance that was implantation bleeding.
If you take a test during the bleeding, however, you may not get an accurate result. That's because it still takes a couple more days after implantation for your body to create the hormones that give you a positive result on a pregnancy test.
When the bleeding stops, go ahead and take a pregnancy test and if it's negative, wait two more days and take another test. If that one is still negative, then chances are you're not pregnant this month.
One more thing - it's quite reasonable to feel pregnant around ovulation. That's because many women (myself included) experience uncomfortable symptoms during ovulation like nausea, lower abdominal and pelvic pain and tiredness. This is just a normal reaction to the progesterone and estrogen (hormones) released during ovulation. Feeling symptoms that early in your cycle doesn't indicate pregnancy so much as ovulation.