Am I in the wrong at work?

Im currently in my second pregnancy but with twins, we are 17 weeks along as of today. I work full time as a licensed veterinary technician, therefore its a very physically involved job. Restraining pets of all sizes, handling anesthesia, working in radiology, handling medical notes, always on your feet, seeing emergencies throughout the day, 10-12 hour shifts 4 days a week, fast paced environment, handling medications, and so much more. Ive been in this field since I was 14 so Im very used to the requirements to this job. I have never had a problem with performing my duties. Even with my first pregnancy with a singleton baby, I pushed to keep going and keep working until 3 days before I gave birth. Im also a full time mom to a 3 year old, and thankfully am able to take our daughter to my parents house for daycare while we are away at work. When Im at work, recently I have noticed that I have become out of breath faster than I did with my singleton pregnancy and more exhausted by the end of my 10-12 hour shift. I lose my train of thought occasionally because Im doing so much sometimes, which is probably just "baby brain". Im becoming larger faster in my abdomen with being pregnant with twins so there have been a lot of things that I have had to take it easy on. The issue Im wanting to discuss is my work place. To put into perspective, my manager has never had children and has decided to have surgery last year to ensure she never has kids. Im cool with that, its not my decision or my place to dictate how she lives her life. Shes still young, Id say in her late 30s however, so we still get along decently. During this pregnancy, she has made it apparent to tell me that Im working slower than usual and would like me to pick up the pace. Shes also discussed with me that its been a problem with other employees, and seems like herself as well, that I dont do some of the physical activities that are required and has been a problem that I have asked other employees to help me with those activites. I get backlash on having baby brain too, which is obviously something I cant prevent from doing. Im beginning to feel like this is almost a discrimination against me being pregnant. Ive explained to my manager that I cant do a lot of the physical requirements but I also dont have any restrictions from my doctor, I was told by my doctor to not do things that are uncomfortable and stay safe with what I am doing. No doctors note indicating that as well. I feel like Im being judged for not being able to perform at the same rate I could before getting pregnant. There are only 5 or 6 other moms in my workplace, but I am the only one that has been pregnant with twins. I feel like I get a lot of judement from my manager because shes never experienced pregnancy. Im expected to continue to work when Im sick. Im expected to continue with my physical requirements because I dont have a doctors note. I feel like Im getting pin pointed out because Im the only pregnant one and have been the only pregnant employee at this hospital since they opened the business 4 years ago. I certainly dont feel comfortable risking my health or my unborn childrens health just to meet the requirements at work. I feel like there are plenty of other employees that are more capable of handling the physical things I cant and it shouldnt be a problem with me asking for help where I cant step in, even if it is still "early in the pregnancy". (I should mention I am technically half way into my pregnancy because I am having multiples) Im not sure how to discuss this with my manager, and/or the HR department. Am I wrong for feeling this way? *Yes I live in the United States and I have looked into my state laws for working pregnant women, but it doesnt give a lot of light on this situation specifically. Im just looking for advice from other people and see their thoughts on this is.