I completely understand what you are going through and it is honestly awful. I am 17 and deal with thinking I'm feeling s* every day as well since I have a sensitive stomach (probably due to the constant anxiety) and I am never sure whether the stomach pain is going to make me s* or if it's just something harmless (and it's always nothing!). I developed the phobia when I was around 7 years old and I have no idea how or why it began because I haven't had to v* since I was 5 years old. My phobia has been going on for so long and has all the sudden gotten worse at this age. I totally understand your embarrassment and I also tend to need my mother to reassure me that I'm okay or just be with me when I'm afraid I'm sick. I am a senior as well and I just want to be able to enjoy my life and have joy and do everything my friends want to do. But this phobia is crippling and I'm always afraid someone is sick and that I could catch it too.
But there is something that always comforts me during anxiety attacks. I listen to worship music (Especially Bethel Music and their spontaneous worship songs that you can find on YouTube) and I talk to God. Praying through this and asking God to fight through my anxiety has helped so much. I think it is mainly a fear of losing control and when I just surrender and realize that God is control, I know that with His strength I can do all things and get through all things.
I'm so sorry that you are dealing with all this as well but it is so nice to hear that someone is going through exactly what I'm going through and that I'm not alone. Just keep pushing through, and every time you get through the anxiety, that is a victory that you can look back on and realize that there was nothing to fear, even though it is so hard sometimes.
Also, I usually just try to reassure myself that what I am feeling is just my anxiety and sometimes I'll just talk to a friend and get my mind off things by laughing and trying to pretend I'm fine (because I always am even when I think I'm feeling s*). So keep fighting, you got this and you are never alone.