Spotting/bleeding can sadly mean something or nothing.
With this pregnancy I spotted for weeks in my first trimester, nothing heavy, light (only noticed on bathroom visits), change in colour (pinkish, red/watery, brown/yellow)
Cramps sadly are very much part of pregnancy too - not good when you have spotting with it I know

pain that makes you curl in a ball and/or pain in the shoulder accompanied or not with clots should be seen to straight away.
Wishing you lots of luck at your ultrasound tomorrow.
x