Either case is possible. OPK's as joyrenee said, can be difficult to read. I had a heck of time with them until I switched to the Clear Blue Easy Digital (different from the clear blue easy). They give you an absolutely obvious reading with either a happy face for a positive or a blank face for a negative. Also, keep in mind your cycle may have changed a bit, so make sure you start testing for your LH surge a bit earlier then you might of. Also, not a bad idea to talk to your OB, and perhaps meds to stimulate ovulation may be required, just to "kick start" things.
I am so sorry for your loss. Please let us know how you are doing. Take care.
OPKs can be very inaccurate. You can use OPKs with another method of determing your fertility for increased chances. You can use the BBT method (taking your temps) or you can use the CM (cervical mucous) method. I personally find the CM method to be easiest. Basically when you see eggwhite cervical mucous, have sex!
You could also be getting negative OPKs because your cycle will be a little messed up since giving birth. I am so sorry you lost your son and please know we're here for you!