If you suspect that you have a problem with rising damp there is absolutely no substitute for a professional survey to determine the cause of this. You could use an inexpensive electronic moisture meter to check the condition of your walls.
If you are using a meter you should start by working on the inside, you need to take readings at regular intervals along the entire length of the wall, not just in one place. You will need to systematically check an area extending from floor level to about 1m above the floor.
If there is a presence of a rising damp, the meter should indicate a high moisture reading, if you check above this level you will more than likely see a drop in readings. Penetrating and condensation does tend to show up either as isolated patches or as dampness that extends right up the wall.
If of course you suspect rising damp, check that there is nothing bridging a perfectly sounds damp proof course before committing yourself to the cost of installing any new one.
It is sometimes possible to detect symptoms of rising damp even after the installation of a new DPC. This is almost always due to old salt contaminated plaster, which should be removed and replaced with special renovating plaster.