why am I suddenly needing to add constraints in Inventor?

for the last several weeks, ever since I started using Inventor for my graphics class, I've been able to easily make 2D sketches and extrude them just by drawing lines. I start one at another's endpoint, make a rectangle or triangle or whatever, click "finish sketch" and then it lets me extrude. Suddenly today, it won't recognize closed areas unless I add "coincident" constraints. Also, half the time after I add the constraints, the lines jump to a spot that's clearly not attached and not making the triangle that SHOULD be easy to draw.... I just don't understand why simple sketching has turned into a nightmare. Is there some setting I might have changed?
3 Answers

Hello Allison,
A suggestion for your sketch is to make sure it is fully constrained. You can check the degrees of freedom by using a mouse right click and select the command [Show All Degrees of Freedom] This will help prevent geometry changes when a sketch is inadvertently moved. Also you will see the notation in the bottom right of the status bar stating the number of dimensions required to fully constrain the sketch. Hope this helps.
Regards,
Ivon LeBlanc