Indian Railway Catering & Tourism Corporation [IRCTC] — Lower birth are not allotted

I had booked a two-way ticket from IRCTC and while selecting my berth preference, I had opted for a lower berth. However, I was not allocated a lower berth and this has left me feeling quite disappointed. To add to my concerns, my mother is traveling with me and she is over 50 years old and has health issues. It would have been very helpful if IRCTC had given us the lower berth as per our preference. What is the point of choosing the berth, when the same cannot be entertained?

It seems like booking a lower berth ticket from IRCTC is impossible.