Strictly speaking, there is no such term as blood thickening. There are a few disease states where the blood becomes more viscous than normal due to tumour cells producing proteins (as in Waldenstroms macroglobulinaemia & multiple myeloma syndromes). In any condition where there is loss of fluid from the body (hypovolemia) like protracted diarrhoea, vomiting, burns, haemorrhage etc, there is a shift of fluid and the blood becomes apparently thick. Also, in a condition called thrombocytosis (an increase in a type of blood cells called platelets), there is a tendency of blood to form clots within blood vessels (thrombosis). You need to discuss with your doctor and find out exactly what the problem is.