The above suggestions are all good. I will add a few more.
You can find more info about these at
http://www.ve1zac.com/My%20Receive%20Antenna%20Compendium.htmor googling any of these can give you several weeks/months of reading material....
If you have the room, a 500' to 800' beverage is hard to beat, they can be unidirectional, bidirectional, reversible and can be electrically rotated a few degrees, but not rotatable like a magnetic loop.
Terminated Vertical Delta Loop and the various mutations (K9AY, pennant, Kaz, DKaz, SuperKaz). These are terminated with a resistor, giving a very nice directional pattern, and if you don't have room for a beverage, these give the best bang for the buck.
A pair of short phased verticals. [I have not tried these YET]
A BOG (beverage on ground) or LOG (loop on ground). [very simple and not bad performance]
For any of these antennas, it is best to locate them away from your house to minimize noise getting into the antenna system. I recommend a choke balun near the antenna to keep noise from traveling out to the antenna on your coaxial cable.
Your Antron99 should give decent reception on the MW bands if you have a pre-amp.
Maybe you have a balun in line that does not pass MW signals through it, or maybe a bad connector or cable.