Monastir Offensive Normal

Oh, my. Don't fret, I also had trouble with this one. You essentially need 2 good cav gens to even stand a chance in completing this one. Stonewall +Moltke is doable, but I had to save up for Plumer to clear this. I'm pretty sure I also had Macmahon at that time, though not fully upgraded yet and newly-bought. 
Anyways, what you need to do is just attack the Bulgarian units head-on with your cavalry gens, quickly take the first city, and them proceed to take out the second city FAST. The longer you take, the worse it gets. Reinforcements will come very soon after you are attacking the second city, and I'm pretty they gas your generals, so I was forced to put 2 healing items on my cavalry gens. Though having a arty general like Beseler or Ivanov is better the further you get into the game, as well as in this mission, as you could travel via the mountains faster. The Balkans campaign missions contain one of the more challenging and annoying missions in my opinion, so you may have to play some other missions or do some more conquests to buy more generals before completing further completing any more missions. Especially another arty general to supplement Hotzendorf.