I don't think you can categorically say that there's been an increase in autism over time because there have been so many changes in diagnosis and medicine and in society in general.
Most people accept that there's a strong genetic link. I've often heard of parents getting diagnosed at the same time as their children. The parents have always been autistic so that's a childhood case from the past that was missed.
More children survive who are born premature. Better antenatal care picks up problems earlier. I think there's a higher incidence of autism among these children but I'm not sure.
Looking back there were several children I went to school with who would have had a diagnosis of dyslexia or ADHD if they were children now. As PP have also said, those who obviously had issues were educated separately, if at all.
I think STEM subjects are usually more attractive to those with autism. Women were actively discouraged from these in the past - less so now - so engineers and mathematicians are meeting and marrying each other. This might actually increase the number of autistic children, but I'd hope nobody would suggest that women shouldn't study or work in STEM fields.
Going back 50+ years there was less automation so jobs required more people to do. Thinking of something like farming or factory work, there would have been a role for someone who had left school with no qualifications who was "different". No diagnosis needed or available.
None of these require a particular drug to cause autism and removing paracetemol as a painkiller doesn't leave much that's safe or tested to use during pregnancy. Even if it's not intended to be about blaming women for anything they do/eat/take during pregnancy it always seems to end up that way.