showerhead for showers with little water?
There is a flow restrictor in all shower heads. The usual design is a plastic disc with two or three holes in it.

The maximum flow allowed by law in a new head as offered for sale is 2.5 gal/min. Most people find this adequate, generous but welcome, or even too much. Lower flow shower heads have a more restrictive restrictor (smaller or fewer holes in the restrictor disc) to give a lower flow. Since most people limit their shower by time rather than amount of water, this saves hot water. So the 1.4 gal/min that you have is probably by design of the restrictor and is not a sign of low water pressure.

It is not illegal for a consumer to remove the restrictor and get greater flow. You can probably find a youtube video on how to do this.

EDIT

I got new low flow shower heads (1.5 gal/min, hand holdable with hose) for our house and our old tankless water heater began working erratically. For a long time I didn't realize it was due to changing to the low flow heads. The water heater would shut off in the middle of a shower because the flow rate was insufficient to keep it on. (Tankless heaters have a minimum flow for the unit to turn on and to stay on.)

Once I realized what the problem was I tried to drill out the holes in the restrictors, but this still didn't solve the problem. Once I removed the restrictors entirely the heater would stay on. (A tank water heater does not have this problem. It will deliver a trickle of hot water if that's what you want, or if there is a small leak).

Before I tried drilling out the flow restrictor I emailed a local expert plumbing supply asking about calibrated 2.0 gal/min restrictors -- they replied they had just exactly that. But when I got there it turned out that the ones they had were too large to fit in the cheap ($15) heads I had. I then tried drilling out the existing restrictors, but when my first attempt didn't work I just removed them entirely. I wash our dog in one of these showers and the extra flow is welcome for that use. A flow of 1.5 gal/min is too low to efficiently wash a dog with a thick or long coat. 

These are handheld heads with hose to them and I have since installed the same model in two other houses where they are apparently working fine with the original 1.5 gal/min flow restrictors in place. One of these houses has a tank (40 or 50 gal) and the lower flow will reduce the number of incidences where one showering uses all the hot water. The other house has the same model of tankless heater we have, but that heater seems to be accepting the a 1.5 gal/min head.