Pregnnat guppy help!?

i have a guppy i bought from the pet store about 2 months ago. She looked about ready to into the 3 way breeder so i put her in. I also put her in because i posted a video on youtube and some guppy breader told me to and he has been breading guppys for over 20 years. she will not give birth idk why. She has been in the breeder for over 3 days now but still nothing. the last time i had a water change in the tank was about 2/3 weeks ago. I dont want to do one because it might mess up something(the pregnat female). the temp kinda changes because my heater is mest up, it dosnt stay at one temp, if u turn it on it will keep giving heat untill you turn it off. i usually put it on low and the temp is inbetween 70 degrees to 83 degrees. she tried eating her food 2 days ago but she spit it out then yesterday she ate it, today she kinda nipped at it and didnt really eat mmuch. her gravid spot kinda dissapeared yesterday but its back today. what i mean by dissapeared is it wasnt as big(maybe because of stress?) her belly is big not to big tho but she has a big gravid spot and its black (at the moment.) i dont know if i should add stuff in the tank or what is hould do. She always tries flexing and pushing( bending in diffrent directions.) she dosnt move much eather. why isnt she giving birth im kinda scared. i have been watching her real closely and nothing really happens she kinda started to stop pooping tho. the chemicals i have is 1. salt(already in there) 2. stress coat water conditioner (from like 7 years ago) 3. aquasafe water conditioner (it takes away harmful chemicals and gives the fish a good slime coat. regualer topp fin water conditioner. and some algae contol stuff. i dont know what to do because the light is verrrrrrrrry low (1 small lightbulb.) i am anxious to get some baby guppies and i really want my female to stay alive and not die of stress. ik she is stressed and if there is some sort of thing i can buy or i have please tell me that will relieve her stress. if you want a video of her just comment below . Do you think i should completely turn off the light? turn up the heat and never turn it off so it dosnt lower from 80 to 70. plzzzzz help plzzz