Hi there, I'm 24 weeks and had my pertussis jab on Monday and had no side effects at all. I even went swimming before work on Tuesday morning!
Whooping cough is a serious illness especially in babies/young children where it often results in hospitalisation and occasionally death. I had it as a toddler as I was unvaccinated due to a vaccine scare before I was born. I've been susceptible to bad coughs my whole life and I do wonder if it stems from that experience (Caveat: this is my personal uninvestigated theory!).
The reason the NHS recommend pregnant women get vaccinated is to protect the baby who can't be vaccinated until after they're 2 months old. See: www.nhs.uk/conditions/pregnancy-and-baby/whooping-cough-vaccination-pregnant/?. The UK Medicines Agency also did a study of 20,000 women on the safety of pertussis vaccination in pregnancy, see: www.bmj.com/content/349/bmj.g4219
In relation to your concern about aluminium, please remember that the first rule of toxicology (I studied public health) is that "it's the dose that makes the poison". This is important as there are microscopic amounts of many toxic substances in everyday products including food, cosmetics and cleaning products, but they occur in such small doses that it's impossible to consume/ingest enough for harm to occur.
In my toxicology class, we looked at a food scare where an agricultural chemical containing a toxic ingredient had been found in lettuces, but you would have to consume something like 2 tonnes of lettuce a day to reach a level where any adverse effect could be found. Of course this didn't stop tabloid newspapers writing lurid headlines that put people off eating lettuce....
If you want to be geeky look up NOAEL - no observed adverse effects level and LOAEL - lowest observable adverse effect level for aluminium. (I don't know what it is for aluminium in the pertussis vaccine, but I'd be amazed if it's not at or below the NOAEL).
Some information about aluminium in vaccines from an Oxford University vaccines research group: vk.ovg.ox.ac.uk/vaccine-ingredients#aluminium
A study on adverse effects following vaccination with aluminium containing vaccines: www.sciencedirect.com/science/article/pii/S1473309904009272
So you need to weigh up the risk of you being exposed to aluminium in the pertussis vaccine versus the risk of you getting whooping cough or your baby getting it before they can be vaccinated.