rotary downshift

alright here is my sitch ... i did search but only for about 10 miniutes and that proved to be quite usless .. for me atleast perhaps i wasnt searching in the right place howvere on to the problum just the other day my add coolant light came on as it has in the past but hanst for about 4 months .... so i thought nothing of it .. then i started my car again this morning and it had come on again so i did the properthing and checked my resavoir and well no coolant?... and as for my rad well i tryed to fill it but it only took about a pop can worth of fliud so i pu tthe cap back on and then went about my buisness ... now it would seem that even going tseady on the hwy at 120 kmh my temp gauge seems to fluctuate .. never above half but to half and then back down to normal again ... now i was wondering .. does this seem like a water pump issue or a thermostat iussue?.. also id like to mention i dont see any coolant puddles nor can i see it spraying out anywhere ...
any help would be great as its my daily driver and i cant afford to have it out of comission ...
thnx in advance
brian