二零一零年十一月二十二号的问题

Okay todays questions

As usual I will use a mixture of chinese and english to get these across :-)

1) 不过，可是 and 但是 all have the meaning but.  I always use 但是 but is there a time and place for each？

2) 所有 means all.  I think I understood but am I still correct to say "我对海鲜都过敏“？

3）in the dialog there is this sentence:

你这男朋友太挑剔了

why is the 这 there and could it have be 你的男朋友太挑剔了？

4）生活 means life.  Is this just human life or do animails have 生活 too？

5）低着头 has lowering head.  Is there a more colloquial meaning?