3 yr old sleep issues EDIT

My husband and I are on different pages about this so I’m curious what other’s opinions are. My daughter is 3.5 and has has issues with sleep since she was born. Her first year was terrible she barely slept at night and she didn’t end up even sleeping through the night at all until she was 1.5 then still would have random issues off and on. She finally started sleeping better a little before she turned 2 and it was great. Slept great, went down without help, napped great although I’ve had to adjust her schedule plenty of times because any little thing would throw it off but overall she was good. A few months before turning 3 she hit a sleep regression and her pediatrician said the 3 yr sleep regression is normal and could last 4-6 months. Well it lasted about 6 months, it was terrible. Now things are better but she still over the last month struggles about once a week with either taking 3-4 hrs to get down to sleep at night or going down normally but waking around 1-2 am then not being able to sleep again until around 7 am. I cannot figure out what causes it, I can’t find a connection to anything on those days. She’s clearly exhausted and she’s not fighting us on sleeping she just can’t sleep it’s like insomnia. She tells us she’s “just awake”. I asked her pediatrician today and after some more questions she wants to run some labs and maybe try an iron supplement because sometimes deficiency can cause sleep issues. Then possibly a sleep specialist if nothing gets better. My husband thinks all that is unnecessary and was kind of annoyed and said it’s just normal kid stuff and it’s a phase. I have always been the one to actually deal with her not sleeping and I have spent countless hours trying to get her back to sleep (I’m SAHM so I’ve always dealt with nights) until recently he is helping more because we have a baby too. I always felt too like it was just a tough baby phase but now it just seems like she’s getting older and not growing out of it and is genuinely just struggling to sleep so I figure why not look into her health to make sure things are ok. Any thoughts or opinions from the outside looking in?

EDIT Thanks for the responses, a few asked about her schedule, she goes to bed at 8:30 and usually wakes between 7-8 when she’s sleeping normally. We have tried a lot of nap schedules over the past six months because she still needs it, she’s a mess without one and when she goes without one she tends to sleep really hard for 3-4 hrs then wakes up all out of it in the middle of the night and needs help getting back to sleep. We’ve landed on 30 min naps usually between 1-2 pm to keep her from getting so overtired but if she sleeps any longer than that she doesn’t sleep well at night.