First, off, yes, steroid injections can be somewhat painful when you first start them. Over time, your muscle will get used to the oil. Some people are more sensitive than others. A big factor is what you are using. Water based are going to be the most painful. Then test prop is probably going to be the next most painful injection. I would stay away from these things, at this point. For a new user, you really only need to use a long acting test for your first cycle. You will get awesome results. The idea of "stacking" is to add to make your cycle stronger, after you are no longer getting awesome results from what you were previously using. Adding deca now isn't going to make a big difference in your gains but it will introduce a higer potential for side effects that you need to deal with.  A long acting test, like test e or test cyp will be one of the least painful shots. Different brands can be more or less painful depending on how they were made. Geneza makes some great gear. Well dosed and well brewed. I find that they are as close to painless as it gets. 

Here is what I would suggest for a first time user :

1-12

Test E or Test Cyp 350-500mg EW, split into 2 injects per wk

adex .5mg 2-3x wk to start, increase or decrease if needed

2 wks after your last shot, PCT starts, Nolvadex 40mg for 1wk, then 20mg for 2 more wks