Question: Pure blood in urine…quite a lot

I am a 63yr old male and over the last few months I have been peeing blood on average every six wks or so, this problem has just returned yesterday, I am peeing pure blood and quite a lot, I have back ache and a bit of pain in my stomach. I am having problems peeing sometimes go fine and other times can’t go. I am residing in Portugal at the moment but have a months holiday booked for S. Africa this coming weekend, do you think it will be ok for me to go or should I cancel my trip and seek medical advise instead? The confusing thing is that this problem goes away for a number of weeks before returning. I have had blood and urine tests that have come back clear and my doctor said it could be a build up of calcium that can cut and cause bleeding which leaves me very confused and worried.
I do hope you can help.