Blood Clots during Period. It is normal to pass blood clots during menses, as along with the blood the thickened lining of the uterus is also being shed and expelled outside the body. In case the abnormal blood clots during period occur, visit your gynecologist as it may then be an indication of other serious medical illnesses.
And yes, it's still possible that you're pregnant. In a normal 28-day cycle, your period comes about 14-16 days after ovulation. However, unless you are positive that you know exactly when you ovulated, your result could be off one or two days. If you did ovulate on the 20th of April, that is 15 days ago. If you're not pregnant, I would expect you to start your period in the next day or two.
It's not likely, but it is possible. Your chances of getting pregnant just after your period depend on how short your menstrual cycle is, and how long your period lasts. One of your ovaries will release an egg (ovulation) about 12 to 14 days before your period starts. The first day of your period, when you start bleeding, is counted as the first day of your cycle. If you have a 28-day cycle, you'll usually ovulate some time between day 12 and day 16 of your cycle. During your period an egg is usually developing, ready for release mid-cycle. The time it takes for an egg to mature within the ovary can vary. This means that the day you ovulate can also vary from cycle to cycle.