how long since you last checked the coolant? how often do you check it? IE is it not normal for it to lose coolant and how fast did it lose it?
recheck the oil after a long run to get it hot and get rid of any moisture, unless the oil is very coffee coloured dont suspect a head gasket just yet!!!
mine was losing coolant, but seeing the common prob for em where there are no other signs is to weep out of a porus block I decided to ignore it

till I had the starter out and couldnt see any leaks so pressure tested it and found the top hose a bit loose, so it can always be the simple things