I dont understand why people quickly jump to the thought "can i sue for this".
You switched pills. You are also in charge of ensuring you are taking the right things. If you knew it was a lower dose, it was your responsibility to question it and to see if it needed to be changed. Did you ask about needing to use a condom during the change of birth control pills?
Birth Control never claims to prevent pregnancy 100%. Even if you take it correctly there is always that very slim chance of failure. You could be that 1%.
You dont even know if you are pregnant and you are jumping to "can i sue". Your period is late? Maybe it's just the change in birth control that has changed your period. Some birth control make periods lighter, even skip periods.
Are you going to think maybe i could sue the birth control manufacturer because my birth control failed?
Sorry, i dont mean to be rude, but you are jumping to 'can i sue' and you dont even know if you are pregnant. Failures happen in life and you should've been aware that birth control does not prevent pregnancy 100% and if pregnancy was not wanted, then a condom should've been used.
Take a test and go from there. If you are not pregnant, it could just be the change in birth control pills. If you know for sure they are lower dose, then go to the doctor and question it. Most birth control, even low dose that can be used to treat acne will still prevent pregnancy adequately (apart from normal failure rate).
Before jumping to conclusions, find out if you are or are not pregnant first. Then go from there. How will your relationship change? The relationship will be how you and he make it. It is you guys that are in the relationship, it is both of you that decide how the relationship goes. How relationships change when it comes to pregnancy and children, depends on the couple themselves.
Edit to add re your updates:
Your mother made you change --> this is no fault of your doctor.
You need to talk to your mother, why she made you change and why she said your previous one wasn't working. Finding out why she thought that. Did you say things that made her believe this, did you have side effects etc. You have only been on the new birth control for 2 months now. The change can affect your cycle/period, its common. Birth control after all contain hormones which alter your body and may disrupt your normal cycles for a short time. Even if the birth control does not cease periods, it can still alter your cycle for a short time whilst your body adjusts. Your other symptoms could also be caused by the change in birth control and your hormones. But if the symptoms/side effects continue, then you may need to change your birth control as this one may not be for you. If you have researched and found that it is lower and has a higher failure rate, talk to your mother and explain your concerns, also use condoms also as an added protection. It seems weird that your mother would want to change your birth control for no 'real' reason.
Talk to your mother, take a pregnancy test and go from there.