You're going to love this answer! What you're describing it totally normal, its the actual sperm in your ejaculation. One of the things no one ever really tells us is that an ejaculation contains two types of fluid. One, the seminal fluid is that whitish creamy colored stuff that we usually have more of. The other, our sperm, is usually jelly-like in consistency and yellowish in color. So, as you're already noticing, the amount of sperm changes from one ejaculation to the next, that's why you'll see more or less depending on how many ejaculations lately etc. So, rest easy my friend....and remember....that yellow stuff is powerful when placed in the correct location! Be careful!!