This is why I am worrying - I just read this article at Miscarriage help and advice

And I quote: 'What are the symptoms of miscarriage?

If you notice any unusual back pain or abdominal pain which feels similar to a menstrual cramp, this may be an indication. Other symptoms are bleeding, pink or grey coloured mucus, contractions which occur at regular intervals or any clots or unusual tissues passing from the vagina. If you are experiencing any of these, they may be warning signs you may be about to miscarry, call your doctor and rest as soon as you can to minimize the risk.'