Downward dog help!

Just to preface I’m sorry if this is a stupid question. 😭

About 6 months ago I fell in love with hot yoga classes. I never did yoga before this really. I go 1 or 2 times a week depending on my schedule (I have 2 jobs and live in the middle of nowhere so it’s far away, I’d love to go more in the future). Anyways! I REALLY struggle with downward dog. I’m talking I can only hold it for a few seconds. The rest of the time I just I just rest my knees. Is there any advice for this? I’m assuming it’s because I have poor upper arm strength, but I have seen little/no progress in this. I am slightly overweight, hoping losing some weight will help too but really just curious to any other suggestions. Thank you yogis!!