Chevrolet: Thermostat Problem Chevy Venture 2003, chevy venture, engine temp

Question
I have a 2003 Chevy Venture.  I believe that there is a problem with the thermostat.  It started this winter when the heater would stop working unless you were pressing the gas pedal.  Engine temp would be normal.  It has progressed to the engine temp climbing into the red.  The fan kicks on but temp still increases. Today temp increased almost to red when I heard a click and then the temp dropped to normal.  Any suggestions or comments on what is up with my van.  I am stationed in Italy and my resources for maintenance are very limited especially for an american made car.  I need to be pretty sure that this is the problem BEFORE I take it to a mechanic to get fixed.

Answer
Elizabeth;
        Well first off are you in the ARMY ? and a NCO or  a officer ? only kidding and good for you I think  everyone should go into the service  I did back in the olden days V.Nam time,  I was drafted in 69/70 so I joined for 4 yrs. I got hurt and got a early out. my Son is in the Marines 5 yrs. now and re-uped for 2 more a M.P. Well what you tell me could be a few things , when was the last time the rad. was flushed and new coolent replaced. and how are all hoses no leaks. Is the rad. cap any good as it alone can cause you trouble. Is the belt or belts good. and the thermastadt
can also cause trouble. I do not think it should cost that much even over there .USAEUR .try to find  someone that will do it cheep or a buddy , etc.  ok and again it should not cost that much for a therm. and a flush and even a new cap too.I would guess at around 150.00 give or take.so do not get taken ...
Roger J. W. E-5 / 15El9 / 42B. Regular ARMY...  LOL...