There is such a thing as arousal fluid, which Creighton teaches to identify, but it shouldn’t be confused with cervical mucus. Here is a little tip to identify the difference:
Arousal fluid (like semen, in case you’re worried seminal fluid is cervical mucus) will dry up very quickly on your finger. It is usually clear and watery, but it can be dissolved in water (unlike cervical mucus). Dip the fluid on your finger in a glass of water and see if it dissolves. If it’s mucus, it will ball up and sink. If arousal fluid, it will mix in the water and be gone.
You may also be seeing seminal fluid and confusing it with tacky mucus. Seminal fluid will also dry quickly upon your fingertips and is more rubber-like then the softer cervical mucus. Also remember that CM is more like egg whites in consistency and color while seminal fluid is generally white/off white without a lot of clear substance.
If you want to practice Creighton for NFP, an instructor will show you a booklet of how to discern all of this. They also will give you some instructions on expelling seminal residue and suggestions as to when to have intercourse so as to avoid confusing CM and residue.