1991 Honda Accord engine cooling

Hi I have been driving my 91 Honda Accord for about 6 months now and for some reason for the past couple months it's been running hot, it doesnt completely overheat it usually runs at exactly halfway between hot and cold on the thermostat, but now it's running like 3/4 of the way, it doesnt smoke at all, and doesnt leak anything ive checked, and all the hose clamps are tight as far as I can see, and sometimes it doesnt get hot at all so im stumped, was wondering if you had any ideas of why this is happening?