It sounds to me that you're doing fairly well. You'll have to judge when and how your combos will serve you. My tactics change when I'm facing differents mobs and different numbers of them as well. If DPS doesn't attack my target, I will often switch in between mobs to build combos on all of them and throw in a flash for extra enmity. You'll have to play around and definitely keep your eyes on the enmity guage near the names and move accorindly with it.
One thing you may want to do is pull mobs (watch which are connected so you know which ones will come with it) with Shield lob.
I can't remember the level 44 dungeon off the top of my head, but I do remember the monsters hitting hard around that level. Keep Shield Oath up at all times, or your healers won't like you.
Aside from that, really check your gear and make sure you're set up with good stuff - AF is just around the corner for you. Those will suffice until you start farming for Darklight.
If you've gotten yourself in check with tactics and gear, perhaps your not the issue. DPS attacking/pulling other targets make things difficult as well as healers not being sure what they're doing. You'll have to judge accordingly and try to be on top of things. You're a tank and may be the defacto leader in some instances. If you mess up (like I have numerous times), fess up and apologize, yet also be respectful when suggesting things to your party members.
I'm rooting for you and I hope you figure out whatever is dragging you down.
FFXIV: Fat Chocobro (Balmung) Level 50 WHM, SCH, BLM, PLD -- MIN, GSM,
FFXIV: Fat Chocobro (Siren) MNK: 21