ually all the time?

Yes, this is completely normal for an 18-year-old male. It is millions of years of evolution telling you to impregnate as many fertile, healthy, young females as possible as often as possible. It is inconvenient to say the least. I strongly recommend that you apply whatever social skills you may have to form a loving mutual relationship with one of these attractive young ladies. It is likely that you will have several such relationships over the next few years and I hope you will enjoy them as much as I have. Save the impregnating for later, of course, but love and are among the most important things you should be doing in the next several years. God (or Mother Nature, if you prefer) is telling you that it is time!