I have seen the doctors many times, but all of these do not work.they couldn't help. I have seen doctors many times, but they couldn't help.

I'm guessing "all of these" refers to the doctors, so I changed it to the plural "doctors".

I have seen the doctor many times, but allnone of these do notir advice works. I have seen the doctor many times, but none of their advice works.

By "all of these", I am guessing you mean all of the doctors' advice. I am also guessing that none of their advice works.

I have seen the doctor many times, but all of these do not workthis has not helped. I have seen the doctor many times, but this has not helped.

I feel so frustrated and have no idea what to do (now/next). I feel so frustrated and have no idea what to do (now/next).

I feel sovery frustrated and have no idea what to do. I feel very frustrated and have no idea what to do.

It is better to use "very" for written English.

My feet have been aching from time to timeon and off for a long time. My feet have been aching on and off for a long time.

Use either "on and off for a long time" or simply "from time to time".

My feet have been aching from time to time for a long timwhile. My feet have been aching from time to time for a while.

Your sentence was grammatically correct, but it feels more natural to not have "time" three times in one sentence.

But I have no idea'm not sure when ithey started like this. But I'm not sure when it started.

"I have no idea" sounds like you're talking about something separate from yourself. "I'm not sure" or "I don't remember" or "I didn't even notice" would be better.

But I have no idea when they started like thisto ache. But I have no idea when they started to ache.

Because this is a new sentence, it is better to repeat what happened to your feet.

But I have no idea when they started like this. (or: when this started) But I have no idea when they started like this. (or: when this started)

Insert a space before “but” (after the period at the end of the previous sentence).

The ache will be reducepain gets better after I have a good rest or have a hot (warm) feet soak; the ache will be increa, but it gets worsed after I do even some very light exercises. The pain gets better after I have a good rest or have a hot (warm) feet soak, but it gets worse after I do even very light exercises.

The ache will be reducesubsides after I have a good rest or have a hot feeoot soak; however, the ache will be increased after I do even some veryorsens even after I do light exercises. The ache subsides after I have a good rest or a hot foot soak; however, the ache worsens even after I do light exercise.

"Subsides" is better to use. It means that the ache is still there, but you can't feel it. No need to repeat "have" twice. "However" is more natural to have even though your sentence was correct. The future tense should not be used because you are not making predictions but stating what usually happens.

The ache will be reduced after I have a good rest or have a hot feet soakoot bath; the ache will be increased after I do even some very light exercises(s). The ache will be reduced after I have a good rest or have a hot foot bath; the ache will be increased after I do even some very light exercise(s).

The ache is localized to thein my heels and the soles. The ache is localized in my heels and soles.

You wrote "feet" earlier, so I'm guessing you mean both sides.

The ache is localized to the heel and the sole. The ache is localized to the heel and the sole.

Nice vocabulary!