Hi. It actually sounds like it could be a hemorrhoid. It's best to allow your doctor to diagnose but here are a few things that might help you out.
Hemorrhoids are generally located in the anal area. It's like a bit of puckering tissue that protrudes from the anus, with said tissue feeling tender, sometimes bleeding a bit, and it can feel as if a small bit of inside tissue from the anus is now on the outside and/or as if the tissue around the annal area has actually swollen to where it feels as if a small piece of the intestine is trying to protrude out. Often they are very painful when irritated or inflamed and sometimes they will bleed.
You have one thing definitely on your side and that is the fact that you have a high fiber diet. I'm also vegetarian; however, I do occasionally eat seafood and a couples of times a year I can't pass up a steak. (grin) Often, hemorrhoids are the result of the need to push constantly during problems related to things like constipation, a natural (and/or concerning) part of pregnancy especially toward the end and during labor and delivery b/c of the pressure of pushing, and it can be aggravated by lifting weights and even cycling if you do not have a comfortable seat.
The first thing I would do is make an appointment with your general practitioner as this doctor can diagnose hemorrhoids and offer medication and advice on how to prevent the problem from becoming worse, figure out if there are any problems on the inside that might need addressing from an emergent standpoint, and keep a check on the problem over a long period of time just in case the problems become worse. There are times when surgical intervention is required if the hemorrhoids begin to bleed. My mother's current husband began bleeding profusely because his had become detached from the inside and was coming out. This was an extreme case and it was an emergent surgery; however so successful he has not had any problems since after following a strict diet, watching the amount of weight he lifts, and is careful with sitting arrangements because certain types of seats, constipation, and other things can complicate problems.
In the meantime, if the area is painful or sore, you can purchase a couple of different products but what I found most comforting for the discomfort and sometimes pain from what I suffered throughout two long yet high risk pregnancies were these Tucks Pads that I used each and every time I went to the bathroom and I added a lot more roughage/fiber to my diet than I had before along with lots more water. Dehydration can exacerbate the problem too.
Warm sitz baths can help too. These are basically nothing more than sitting in warm to as comfortably warm as you can stand to ease the soreness. I'd also stay off the bike and not lift weights or do any heavy lifting until seeking medical advice and examination from your doctor. I only say this because it's not usually bad but it can go from bad to worse if not taken care of properly especially if it's a first time.
keeping you in my thoughts and hoping all goes well. Please Please seek out your doctor's help to make sure all is well. You seem to have a healthy lifestyle. It may just need a little tweaking to keep you that way.