For about 2-3 months straight now, my toilet has been overflowing/not flushing properly. I'm pretty much sure there isn't a clog because I've plunged it over and over and over again and it just doesn't seem like what I know a clog to be like. After all of this time and all of the plunging and work I've done to fix a potential clog, it just doesn' seem likely that it is a clog. I'm pretty sure nothing was flushed that shouldn't have been and since so much time and work on plunging has gone by I really don't think a foreign object or clog is the culprit at this point.

Half the time it flushes without incident and then the other half of the time the water in the bowl just doesn't recede, it fills up and will overflow.

It seems like there is no downward suction. It seems like it has no downward "power" whatsoever. It just kind of immediately fills up, and will slowly drain or a quick one or 2 pumps with the plunger will cause it to drain.

This seems to be a regular winter occurrence. Is there some reason this would happen almost exclusively in winter time?

I have a septic tank.

Thanks for any help.

You have a clog someplace, and you need someone with a snake... not a plunger to find out... is this the only toilet with this problem? If not are the others above or below this one?

You have a clog, a plunger only fixes a small percent of the problems.

Have you ran a toilet auger in toilet yet ?

A plumber may have to come, take toilet up and run a snake down the pipe.

Are any other drains slow if you leave water run ?

Since you are on septic and not city, it may not be a clog. There is a chance that your field lines are saturated and there is no where for the water to go.

When was the last time you had you tank sucked and cleaned?

I had this issue for years and finally resolved it last winter by venting the field lines in one area.