Occasionally, the 副助詞（ふくじょし） (adverbial particle) ばかり is combined with verbs in their 連体形（れんたいけい） (attributive form), to show that (A) is the only thing that is occuring. It may also imply that (A) is happening ‘more and more’, or that ‘it keeps on (A)’. This phrase utilizes ばかり’s standard meaning of ‘only’, and combines it with the 助動詞（じょどうし） (auxiliary verb) だ
The price of gas keeps rising.
Recently I haven't been working out, so I keep on losing muscle.
Japan's population continues to drop.
Because there are so many crimes around here, the public safety of the area continues to get worse.
As can be seen with these sentences, this use of ばかり is paired almost exclusively with verbs that describe some form of change (higher/lower, stronger/weaker, better/worse, faster/slower, etc).
If the speaker would like to express further information in a (B) part of the sentence, だ
will simply get changed to its 連用形（れんようけい） (conjunctive form) で, before continuing.
The reputation of this town keeps on getting worse, and it doesn't look like it will get better anytime soon.
The amount of tourists keeps on dropping, and the stores around us are closing.
This use of ばかり is primarily seen with negative trends. However, this is not a grammatical rule, and positive trends may also sometimes appear with ばかりだ.
Because I work until late at night everyday, I keep getting more exhausted.
Ever since I changed hospitals, my health keeps on getting better.