Our female daschund has reciently started humping our male daschund. Neither dog is fixed and she won't be in heat for about three more months. She is four yrs old and this has just started a month ago...

Don't worry about it. It's very common and usually is a sign of asserting some sort of dominance, although half the time there doesn't seem to be much reason at all. My 10 year old female dog has recently been vaguely humping my female cat, and it seems to be related to jealousy of affections from me.

I would have an err of caution because 4 years is getting a little old to be breeding. Are you planning on spaying? It is a dominence thing, but if you don't want an "oops" litter, I would consider getting both of them fixed, they will be healthier and happier for it!