Two separate things are going on here, and both are common and benign in a 24-year-old. The thinner second part of the stool after prolonged sitting and straining is usually just the tail end of a normal bowel movement being squeezed out through a tightened anal sphincter - it is not a sign of narrowing when the rectal examination by a surgeon was normal. The small reddish fleshy bit that appears on straining and goes back on its own is most likely a first or second degree internal haemorrhoid or a small anal skin tag. The single most useful change is to stop straining and stop sitting long on the toilet - finish within 3-5 minutes, and never with the phone. Keep the isabgol daily rather than twice a week, drink 2.5-3 litres of water, add fruit and vegetables, and a warm sitz bath for 10 minutes helps if there is any discomfort. Since there is no bleeding, pain or weight loss and your examination was normal, this needs habit correction, not surgery. Do get reviewed if bleeding, pain, or a lump that does not go back appears.
Next Steps
Take isabgol daily, increase water and fibre, limit toilet time to under 5 minutes without straining, and use warm sitz baths if uncomfortable. If the swelling or any bleeding continues after 4 weeks, do get examined - you are welcome to consult with me at Synergy Multispeciality Hospital, Miraj.