I have had service calls where the customer complained of a sudden drop in water pressure or a weak flow in the shower head.  I always have to ask, "did you recently change your water heater or have a leaky pipe repair"?. The answer is almost inevitably a resounding "yes". 

When plumbing repairs are made, especially in older homes, pipe crust is dislodged and will clog shower-heads, faucets and collect in discrete places behind the wall where the pipes make sharp turns.  The shower head and faucet filters should be removed and back-flushed, allowing faucets to run opened for a few seconds for removing particles of rust and mineral coating from the pipes and elbows after repairs or tank replacement.

If this doesn't resolve the flow or blockage, shut off the stop valves under sinks and disconnect the feed lines.  Turn on each shut off valve into a small bucket with enough water pressure to flush the valve and the narrow feed lines, then reconnect them and test the faucets. 

If that doesn't work, you may consider replacing that section of the water pipe with something quick and flexible, like Pex tubing, a good replacement for the old stuff.