Good day to all. This is my first time on this forum so be easy on me. I am seeking any advice to what seems to be an intricate and frustrating problem. Here it goes:

Problem:

I have good cold water pressure to 3/4's of my house. Now the other 1/4 of my house which runs to my laundry room, an outside hose bib, and my hot water heater have extremely low pressure. Since the cold pressure is low feeding to my hot water heater I have low hot water pressure EVERYWHERE in my house. I am on a slab so crawling under the house trying to trace my lines is not an option.

Possible Theories:

I am almost 99.9% sure that I do not have a leak because my water bill hasn't fluctuated any in the past year or so, in which is how long I have been dealing with the problem.
Might I also add that slightly before this problem occurred I had my main water feed at my meter ( on my side) bust, in which I had repaired. Is it possible that during the time that the main feed was exposed in the ground, it collected debris and is now jammed up at T? If it is clogged how can I unclog it without ripping down walls and jack hammering up floors? Compressed air?
Is it possible that my slab has shifted and is now pinching a portion of the copper line?

I would like to think of myself as a decent troubleshooter, but this one has me stumped. I don't have much experience with plumbing, but am not afraid to endeavor. ANY ANY advice would be greatly greatly appreciated. Thanks in advance.

Logically your main line should come into your house. At that point there should be a stop valve and possibly a pressure reducing valve. From there the main line (cold) water line should go to your water heater. There may be cold water lines branching off between the main stop valve and the water heater. There should be a stop valve on the cold water input at the water heater. Any blockage would be at a valve. If you have any cold water take offs between the stop valve at the water heater and the water heater itself, they would be affected by a blockage at the water heater stop valve.

Debris could be partially blocking the water heater stop valve. That debris would most likely be solder that ran inside the pipe and fell on to a cold section of pipe if you used an excessive amount of solder when making the repairs.