I Think My Fish Is Sick, Please Help!

I am new to the fish hobby, I've always found something so fascinating about watching an aquarium full of fish, I didn't know that there was more to it than just having a tank, adding water, and then adding fish. I was given a small 5 gallon aquarium 3 months ago and I did everything wrong. In that 5 gallon I had 2 guppies, a Cory, and a black Molly all of which I added immediately, not knowing that I needed to cycle the tank first, I had no idea what that even was. After about a month I noticed my Molly shaking and thought that was odd so I did some research and found out that it was something called the shimmies, and from there I found out about water conditions, and also that I had her in way to small of a tank. So I went and bought a 30 gallon tank, I read everything I could about cycling the tank so that I knew exactly what to do. I let it run adding food to an empty tank for 5 weeks, and did 50% water changes daily to the 5 gallon until the bigger tank was ready. I also bought an apI master test kit and checked the water every other day, I had my ammonia spike, followed by a nitrite spike, and then started seeing some nitrates which I read was okay at the numbers I was getting. I was able to transfer my fish over to the bigger tank and it took a few weeks but my mollies shimmies went away and she seemed to be doing okay, she wasn't using her back end much to swim and always had her back fin clamped and I talked with my fish store and he said that the ammonia spike in my 5 gallon tank probably really damaged her. I feel awful for all she has been through because of my lack of knowledge, so now here I am today, about 10 days ago I noticed a small white area on her head, and it faded away a few days later. But a few days later I noticed her body was white-ish and ahe was kind of acting strange, staying at the top or laying at the bottom of the tank. She still has an appetite and will eat but the shimmies are back, I am at a complete loss of what this could be, I took some pictures the shimmies make it hard to get a clear photo but it's mostly on her tail.
I tested my water last night they were-
pH- 7.2
Ammonia- 0
Nitrite- 0
Nitrate- 5.0

Thank You for any and all help, it is so much appreciated, I really don't want to lose my girl.

 

how often are you doing water changes now?

long term ammonia and nitrite exposure can lead to permanent damage.

did the white spot look fuzzy?

 

how often are you doing water changes now?

long term ammonia and nitrite exposure can lead to permanent damage.

did the white spot look fuzzy?

I'm doing 25% to 30% weekly water changes.
The spot on her head looked a little fuzzy, but what's on her now looks more like a dust covering.

 

start doing 50-75% weekly water changes.

can you get some side shots?

 

start doing 50-75% weekly water changes.

can you get some side shots?

And here is one from juat over a week ago, this is how it started out with a white area by her lips. And this stuff was fuzzy looking, like cotton.

 

i'm not too sure, probably fungal.

you could try a salt bath (aquarium salt, no additives) in a separate smaller container.

https://molliesfish.com/molly-fish-diseases-and-treatments/

1. 1 tsp for every 1 gallon of tank water
   
   
2. Use .03% concentration
   

 

When I started my new 10 gallon tank a few months ago, I didn't know I need to cycle the tank, luckily all of them survived.
I remember my molly fish looked like yours, fins folded, unhappy and nervous.

Do you have planted tank? How do you treat the new water? Tried any bacteria product first?
I wouldn't recommend too much water change frequently. Add some aquarium salt if you want, but you don't have to considering other type of fish in the tank.
Feed them some boiled vegies, pleco wafers, quality tropical fish food, try to make it diverse.
If your fish is still eating, you should be fine, stick with the weekly water change and other stuff, they will become better.

Since you have 30 gallon tank, maybe consider adding more molly fish. I found my molly fish always swim together. I once separated one female because I thought she was pregnant, and she had the shimmies and clamped fins, until I put her back to her buddies.