How long do DVT lasts in the calf? I have a suspected DVT in my right calf?

so much pain when I walk and it is a bit swollen too. I am due to have an ultrasound in the afternoon tomorrow as today they are all booked out. my granddad died of a heart attack and so did my uncle as a blood clot travelled to their hearts, and they were in their 40s too and I am 40. My grandmother died of a stroke as a blood clot went to her brain and she was in her 50s. so I am just woundering how long can a blood clot stay in one place for before it starts to travell and you end up dead? any advice?