First of all, let me say how gratified I am that, though you're still in college, you've found your way to the TI Discussion Forum. As you may guess, most other Forum participants are considerably beyond your years and well behind your speed, but their motivation to swim well and understand the hows and whys is second to none.
Second I'm impressed with your determination to understand why your times improved so dramatically at first, then far less, then not at all. As well, you've posed the implicit question: "Swim beyond college?" I'd like to answer "Yes, yes, yes!" It's far too common for those who finish college to "retire" several years before they've reached their "peak physical potential" which occurs in mid-to-late 20s. If you consider "peak swimming ability" then Dara Torres demonstrates how far beyond college that can continue to improve.
Are you willing to consider the possibility that by pursuing improvement in a more focused way, you might start improving again, and that you might discover you can swim far faster than you can even conceive of right now?
I say this because my college experience was remarkably similar to yours.
I graduated from HS in 1968 with best times in the 200-400 yd Free (there was no 500 in HS then) of 2:13 and 4:53. I'd never swum a 500 or 1000. I did swim one 1650 in an AAU meet (in the days before USA Swimming) with a time of 21:50 to the best of my recollection.
As a college freshman, I went 2:01 for 200, 5:39 for 500, 11:57 for 1000 and 19:46 for the 1650. Sophomore year I improved to 1:55, 5:12, 10:45, and 18:06. Junior year it was 1:56, 5:14, 10:53 and 18:02 (only the last improved from the previous year.) Senior year 1:58, 5:15, 10:58, 18:24. The pain, frustration and disappointment of working so hard -- indeed the slower I went, the harder I worked -- and feeling so hopeless and clueless about having all my times be slower are still fresh in my mind.
The unexpected blessing of that disappointment is that it prompted me to lack of fulfillment caused by the way my swimming regressed the last two enter coaching, a decision that has brought me indescribable rewards. My swimming frustrations also led to the questions about traditional training methods that have been directly responsible for development of the TI method.
And finally, I applied lessons from coaching others to my own swimming, resulting in multiple National Masters long distance championships, national age group records, a medal at the Masters World Championships and being the top ranked open water swimmer in my age group, all since turning 55 three years ago. You can imagine how this feels after feeling so helpless at 21.
Richard and Rhoda have both asked questions well worth considering as context to what's happened with your swimming. For instance, pacing of sprint races is something very few swimmers know how to do. Were your first and 2nd 50s in the 100 less than 2.0 seconds apart? If they weren't closer than that, you spent too much of the race decelerating, fighting through fatigue. Another possible factor is an ineffective combination of Stroke Length and Stroke Rate.
There are many more questions I could pose for you, but I'm glad you've initiated a dialogue and I hope the help and support you receive here prompts you to consider continuing your pursuit of swimming improvement beyond college. You may find that swimming for yourself may be easier than swimming for the varied goals of the college team. It will also allow you to "own" your swimming, to take full responsibility for your training and performance. That can be a tremendously empowering thing.
Head Coach & Chief Executive Optimist
May your laps be as happy as mine.
My TI Story