Oh honey, I can't imagine how hard it would be to let those fears go after a miscarriage. I suffer from anxiety from time to time that leads to panic attacks and it is debilitating and really does a number on our bodies.
Guided visualization CD's (used with headphones) seem to help me tremendously. There are lots that deal specifically with anxieties.
Also, EFT therapy (Emotional Freedom Technique) is something that was practically made for this type of situation. It feels a little silly at first, but it can be extremely helpful. The first time I tried it, I was practically rolling my eyes in doubt the first couple rounds and then I suddenly burst into tears. It really releases pent up emotions and helps you feel more in control - and anxiety/stress occurs when we are losing our control. There are some you-tube videos that show you the points where you tap...the tapping along with a personalized script will help you to tailor the technique to any painful or fearful situation. You can have someone do it to you, or you can do it to yourself. I've done it really quickly in parking lots, in the bathroom, lying in bed...anywhere.
The only other thing I can think of is to be regularly talking with other people who are in your position. This board alone has eased my anxieties tremendously just because I don't know what the heck is going on with my body and somehow, hearing that other women also don't know whatthe heck is going on with their bodies, comforts me. And the laughs that come along with it are nice bonuses!