You've correctly diagnosed the cause of the problem as insufficient signal strength. It's not surprising that you got good reception for a few days but then suffered a loss of signal. It's because the strength of the signals arriving at your aerial can vary quite widely. They're affected by the weather (with, for example, rain or snow obstructing the signal path), atmospheric pressure and the number of hours of daylight in a day (both of which affect the height of the radio-reflective layer of the earth's ionosphere), the 11-year sunspot cycle and individual solar flares on the surface of the sun (which again affect the ionosphere but also create electrical storms which can block signals) ad many other things. The signals were initially strong enough but are now (for the time being) no longer so.
You might need a new aerial. (If so, it's wisest to replace the cabling as well as the aerial). However the fact that your signal strength is nearly good enough for decent reception suggests that a cheap signal booster should solve the problem for far less cost.
Chris