Hi Hammerpgh,
As mentioned by TwoLow & Dave3cu - this problem sounds exactly like pitch/trim - it caught me out in exactly the same way when I first tried FS & usually results in lots of swearing at joysticks.
Unfortunately it is a fairly lengthy subject to teach about - but once you have been told it will all make perfect sense. Here is a good tutorial on the subject:
http://www.flightsim.com/cgi/kds?$=main/howto/trim.htmThe trick is to make small adjustments & the let the plane settle (you can watch the vertical speed dial) before adjusting again if it's not quite right - otherwise you'll end up 'chasing the needle' as they say.
PS: for ease, if you have 2 buttons free on your joystick then you will find it really helpful to assign them the funtions for pitch/trim up & pitch/trim down - maybe with some small stickers on the button to remind you which is which - these two examples (different sticks) made my flying sooo much more enjoyable:

To change the button assignment just go into Settings-> Assignments, then go into the 'Event Category' drop down menu & select 'Control Surface Commands' -> select 'Elevator Pitch Down' & 'Elevator Pitch Up' & assign them to the keys on your joystick:

Sorry if all of these instuctions seem a bit condescending, they're not meant to be - I just like to try & get most of the issues covered incase people don't know - we were all newbies once.
Cheers,
TSC.